I love being a villain. You feel like you are actually a part of the villain world in the DC universe. Also I've been reading a great anti-super hero comic lately; The Boys by Garth Ennis, so I am especially loving kicking super hero butt.
Also, I prefer villains over heroes because I'm an evil bastard at heart... in every movie / TV show / game I'm always cheering for the villain and I'm glad when there is a sad ending (hero dies or something). I am just a bastard, being a villain lets me be that bastard :D
I normally like playing on the villain side and even got a villain character up to 30 here but I gave up on it. Way too many missions were me fighting against other villains and always just getting betrayed or betraying other villains. Now this might be common place in the DC universe, but to me it just got stupid.
I mean, if I'm going to be fighting villains half the time as a villain I might as well just be a hero. I just found the villains here too stupid. If they spent all the time they spend screwing each other onto actually fighting the heroes things might actually get done (like in the intro).
This is what game designers like to call 'balanced gameplay' which roughly translates to 'you can have fun just as long as something's slightly irritating you.'
Go hero if you're playing on Death and Glory; theres a ton of low level villains so its really easy to find people to kill. They hang out in large groups too; which means you wont' have to go looking too much.