WP flares are metal and Bushwacker are plastic so if you like one material versus the other, that will help your decision. Also, I don't know what your local laws are regarding the amber light, but the WP ones don't come with it. There appear to be some optional lights you can get but they look like they just bolt into place where the first bolt for the flare goes which would look like crap, IMO.
I do have to say I'm a little biased though because I just put on my Bushwacker flat fenders earlier this week and really like them.
Bushwacker's $50 rebate ends tomorrow so if you like them I would recommend pulling the trigger asap. I picked mine up from TruckAddons while they were having their smoking deal on them. They still have a pretty good price though (you have to add it to your cart to see the real price).
'09 X Unlimited, 4WD, auto, half-doors, soft-top
RC 2.5" Series II BB, JKS Quick Discos, JKS adjustable front track bar
15x8 Unique 297 (Soft 8), Goodyear MTR/Kevlar 35x12.50R15
5.13 gears, ARB front locker, Currie front shafts
Bushwacker flat flares, Rubicon rails with steps added