If you've been riding sport quad for a while i'd go with the raptor but only if you don't want to put too much work in it. If you want to put some aftermarket stuff on a 400ex and just tinker around go with the 400ex.
I have been riding street for a couple years, now dirt for a handful of months. I know it doesn't sound like much, but I am very aggressive and I learn VERY quickly- so much so sometimes it just downright ticks off my friends. I have been riding a blaster 200 that I bought for my wife... it's not bad... but it's slow for me. I'm use to super sport motorcycles.