I found my favorite race to be Greenskins. Their orcs are really cool looking, love their goblins and being able to use goblins to attack the enemy from behind has proven useful many times. Their monster units are awesome as well. Plus Grimgor Ironhide. My favorite legendary lord in the game. The units aren't really weak compared to vampire units (their units kinda suck. Ethereal units die fast, and no idea still what Black Coach is for. Seems good against hordes of troops, but still a weird unit). Vampire has good flying units however. The vampire flying units pretty own, especially during sieges.
As for Greenskin units, they do have low morale which is a downside. So have to micromanage them to keep sending them back to attack. The morale recovers fast though. Vampires have to deal with crumble though, which is WAY more annoying than the Greenskin morale. Oh and can't forget about giant *** spiders that Greenskins have....best unit in the game
Overall I just love the Greenskin artstyle.
Second favorite is a toss up between Empire and Warriors of Chaos. On one hand, I love using WoC units in battle, on the other hand, their campaign gets boring fast. Even with a mod that lets them settle, its kinda meh cause everyone hates you (which makes sense, no problem there), but not my type of campaign. Chaos units are my 2nd favorite though. Empire has an awesome campaign, but really, who wants to play humans when you get awesome races? Probably same people who choose human in world of warcraft
I can see though cause the Empire does have an awesome campaign, with the most boring units...except...karl mother****** franz.
Last are vampire counts. Which is funny, since I thought they'd be by far my favorite race in the game. I like playing their campaign spreading corruption, but I don't like playing battles with them at all. The most fun with them I have is getting flying units and owning everyone in sieges. But I find more fun overall with the others. Mannfred is an epic legendary lord though, my third favorite legendary lord in the game.