Oh gawd. Either are fine. I put it this way, if anyone is buying a GTX/XTX, then they must have a decent PSU already, ruling power out - I mean what actually is the difference? GTX, must be about 95W full load maybe, the XTX, probably about 120W. Those figures are roughly right. Wow, 25W! The heat issue is far more important. Then again, the ATis use direct heat exhaust, so a lot of dumped out of the case and the nV's don't seem as efficient at this, so they turn up almost equal heatwise. And I must say, people, if it's stable, does it matter the temp? I'm sure some people must watch their temp monitoring programs the way they go on. I admit, if you have a SFF, then the nV is probably the best way to go, however, most of us with ATX cases know good airflow is a must. I don't think it's that productive arguing the same point over and over. Has someone calculated the specific air temp difference? I'm sure it would only be say 3C max as air has a decent heat capacity and flowing air can draw a lot of heat away (hence the need for decent airflow).
I say, buy whichever is cheapest reasonably and suits your needs in terms of the games you play etc. IQ is practically the same, everything is the same. If you've had nV, stick with it - it's so much easier. When I made the jump from nV to ATi after the FX farce, I couldn't get anything right (drivers etc).