truvativ all the way i say. they have the best feel to them and oversized. i have them on Jump bike and DH bike. i have a medium rise 720width bar an dh bike and i love the feel of it. and they really strong!
Lower bars mean you'll be getting your weight over the front more and giving the front wheel more traction, high rise bars can make you sit more upright, but it's what makes you feel comfortable, so don't get too carried away with fashions. Wide bars are good for carving the bike through turns as you've got more leverage and give a greater feeling of control. You do get caught up in trees if you're not careful though! Sunline do some nice 27" low rise bars and RaceFace do the Atlas too if you go down that root.
If you dont have trouble getting through trees then a wide bar is much better because you have alot more leverage. but if you need to pick through trees, a thiner bar can save your knuckles
chromag makes a bar with almost no rise (fubars OS) which is suposed to be awesome easton makes an awesome handlebar, the ea70 comes in a low rise and it feels almost perfect, the only thing is that it only comes as wide as 27"
Forks keep getting longer, so it makes sense to lower your bar to keep your hands in the ideal position.
I'm running a Funn Fatboy at 28" wide with 1" of rise and a direct-mount stem (stock Sunday Elite). My grip height is a couple of inches lower than that of anyone else I've met (given similar bikes) and I wouldn't want it any other way. I'd even consider a flat bar if it didn't interfere with my fork's stanchions, but I'd only recommend going all-out low for someone who's not especially tall or has a super low bike, such as the Sunday. A direct-mount stem and flat bar on a bike with a 15.5" BB would feel all wrong.