I've had both... well alot more than just both brands
eVGA GTX 285
MSI GTX 260
BFG 7800 GTX 512mb
Albatron 6800 GT
PNY 5900 Ultra
eVGA 5700 Ultra
My point of telling you all this... I've gotten basically the same hardware from EVERY manufacturer. Reference pcb with reference cooling... with only slightly higher than reference clocks... nothing I couldn't have done on my own anyway.
Go with whatever has a better;
That's really all I can say... Step-Up is nice but no one I know who's had an eVGA has been able to take advantage of it.
As far as customer service... I can't say much about any of the brands i've owned... all cards have been flawless and I never had any issues. In fact the 260, 6800 gt, and 7800 gtx are still being used by my roomate, sister, and a friend... that's going on 4-5 years on the 6800 GT... to really ever have to deal with custom service you'd have to be really unlucky.
TLDR version... go with whichever has a cooler looking sticker