With regards to the XSPC kits, I believe they are supposed to be very good, but my understanding is that the reservoir/pump combo is the weakest element but still reasonable.
I got one of the older kits (the one before the RASA) and the installation instructions weren't fantastic, but i think they were good enough.
If you can afford it I'd go with rjkoneill's suggestion and get one of the OcUK assembled kits.
But I guess it depends if you're like me, I'm happy with something for a little while, then start wondering if I should've bought the next model up. For me the OcUK kit would be best as there wouldn't really be much I could upgrade (except for getting a GPU block), so it'd work out cheaper.