The empires core are not the best out there but on the other hand there are cheap with a decent variety, there also have core knights with a 1+ armour save. Core knights also allow you the tactical option of an entirely mounted army. The combat infantry are poor compared to most other armys now, however static combat res can be enough to win many combats. My personal favourite are swordsmen the higher weaponskill and 4+ save in combat lower casualties, however within our gaming group halberdiers have legendary good luck. For detachment I usually take 9 halberdiers or free company, I deploy these in a 3 by 3 square for easier movement and counter charging.
Missile troops I find vary in there usefulness depending what army your facing the basics are handgunners vs armour, crossbows for range and bows for movable shooting. Also huntsmen your only scouting units useful to try deny your enemy scouts postion and slow down units by preventing marching and don't forget 10 S3 shoots can damage elves. We play on a 6ft by 4ft board and I find 30-40 ranked up shooters is the maximum worth taking, remember skirmishing units (archers) can bring more shots to bear.
My first choice of special unts is usually a cannon followed by a mortar or another cannon depending on the enemy. My next choice is usually pistoliers there are an excellent harassment unit, march blocking, attacking warmachines, pistol shots plus 3 attacks each (including the horse) make them a decent low cost unit. I also like outriders against certain armys but there a prime target for armys with there own shooting.
I am afraid greatswords (or goldswords) do not feature often in my armies stubborns good but the current fear rules and there lack of killing power often see them outdone. Also for an elite infantry they only have 1 attack meaning the many 2 or more attack infantry out there butcher them very rapidly. I find a small unit of 10 sometimes useful if the slot is free.
I love the empire rare choices although you need horde based infantry armys to get the most of hellstorm rocket batterys. Steamtanks are excellent though some armys have characters or metal magic which will make mincemeat out of it, also watch out for warmachines a few bolt throwers, cannons and stone throwers can quickly cause those few wounds that render the tank ineffective. Volley guns on a good day are lethal to anything and your enemy will go to some lengths to get rid of them use them to funnel his units to where you want them, also if you have 2 or more make sure you postion them to be able to concentrate fire. Also use them to scare off any flying nasties. Also remember occasionally its worth moving them to get in range if there are no good shots.
Flagellents are a good unit but I find it better to take a warrior priest enabling you to take a unit as core.
All the lord choices have there uses and I find you have to choose one to compliment your tactics, the only one I do not use really is the arch lector (I find Volkmar is better if I want to go down this path).
If I use an elector count mainly for the leadership bubble, remember you may as well mount them for the improved armour save (even in infantry you can not target them with most ranged attacks) and I take items to improve there survivabilty such as the enchanted shield (0+ save), holy relic.
A Wizard Lord can add to your ranged attack power the lores I usually go for are fire or metal other lores can be useful but depend on your enemy and the terrain, also a few bound items add a bit more to this.
The Grandmaster can be useful in a fully mounted army but I find this tends to push the army towards a "super unit" and this has gone wrong a few times for me, a few lucky shots, magic or anything else can seriously hurt this kind of unit.
Of course if you have gone combat strong or have stubborn troops a captain with a battle standard can be invaluable.
Warrior priests add that little bit of combat power to a unit of knights on the charge with the hatred rule, they add a dispel dice and have some spells which if you can get off can be extremely useful (healing the emperor's wounds back to full and D6 S4 no armour save hits is always good).
Wizards are always handy if only for dispel scrolls. Remember if you mount your wizards (or engineers) there US2 so with a warmachine crew that's US5 enough for a table quarter, but on the downside enough to cause panic tests but i have used this ploy in the last turn a few times to scrap some extra victory points in.
A Captain mounted on a pegasus with basic equipment is cheap and should be able to hunt down wizards and warmachines, you can add to his harassment value with items such as the doomfire ring, sword of fate or the casket of sorcery, beware of shooting though.
Engineers are for me more of a fun character when I have a slot unused though a BS4 volley gun can be useful. I equip them according to what machine I intend them to accompany a repeating pistol for volley guns or where you will probably use there special rules most turns, otherwise give them something else depending on your enemy, pigeon bombs can be deadly to elves and a few good hochland long rifle shots can bump off an enemy wizard or the odd champion. This is more a lucky bonus though then a certainty. Remember pistols can always stand and shoot too with a lucky shot you can finish off some small units.
All the empire special characters are good, like super versions of there normal counterparts. I can not fault any of them except for being a little bit expensive sometimes.
Karl Franz well I always take the hammer 25 points for D3 wounds is usually worth it remember they FAQed challenges so it can add to overkill too, plus he has a decent chance of killing anything he charges. Add in magic res and a 4+ ward with the 18" leadership bubble well he is the emperor after all! Mount wise I either go for the warhorse or the Dragon, I find Deathclaw gets shot down a bit too much but I suppose against armies with little or no shooting deathclaw could be useful. I avoid the dragon with armies which have bolt throwers or other warmachines as this tends to hinder your mobility whilst you take care of them and does not allow you to get full use out of him.
Balthasar is another excellent choice particularly against armies with heavy armour due to the lethal spirit of the forge spell. With a 3+ ward save against shooting (remember this extends to his mount too) and magic res 1 some armies struggle to pin him down allowing him free reign to cast his spells of destruction to his hearts content. A good wizard lord choice but only I find against certain armies.
Kurt Helborg if you take this guy you have to ensure you charge! With his combination of items plus the weight of a unit of knights most probably he will cut most units to bits. That said beware unbreakable or large stubborn units, also assasins he has only a 2+ armour save to protect him.
Volkmar is useful is a mostly mounted army giving multiple units hatred is well worth it, plus the spells he can cast can be powerful. The only downside is he is on his own the War altar cannot join units, making him a target for ranged attacks. Also careful postioning and forward planning with his movement is needed as he is frenzied and has to charge! Also beware S7 attacks as these can destroy the altar (though at least it gets a 4+ ward save) losing the war altar also looses most of Volkmars powers and items as they are tied to it! Against the right enemy though used wisely Volkmar is deadly.
Empire Army Styles and Tactics
There are a few common builds I use some with more success then others. Mostly these days I take a combination of the basic tactics in my army say combinging the gunline with charge! tactic for a kind of refused flank.
Gunline as the name suggests pile up the handgunners and warmachines throw in a few wizards and try to vaporise what ever comes near you. On its own i find this tactic rarely works with no combat type troops any half decent enemy troops will eat through your gunline with ease, secondly some armys like Brettonians are on your so fast in such numbers you have no chance of taking them down. Terrain can also place a big part with this tactic an open board can leave you vunerable, a hill and some terrain to slow or bottle neck your enemy can make it lethal.
Charge! mount evereyone up and charge hell for leather at the enemy, remember it limits both shooting and magic (most magic anyway) when units are in combat plus empire knights are cheap so they will be numerous Volkmar, Kurt Helborg and Ludwig are all good additions to this kind of army. I have had numerous victorys with this type of army but some armys are just too tough, superiour in combat of unbreakable and numerous (damn those vampire counts) to beat.
The Lure combines a small gun line with warmachines with Knights or fully ranked infantry waiting to charge and obliterate the survivors, against armys with little ranged attacks outriders are an excellent choice for the gun line as they can just whip off when the enemy draws close. Postioning of units and sometimes sacrificing shooting for movement is also important. If you go for infantry remember detachments (like units of 10 handgunners) do not cause panic this can be invaluable.