I repaired xboxs for a while there. Pretty much any xbox without hdmi will fail regardless of how you treat it. They are basically all xenons(first motherboard, 203w psu). The first gen hdmi xboxs were pretty bad also this was the zephyr motherboard(203w psu, hdmi). The second gen was hdmi falcon motherboards. they were pretty good. If you treated them right, they didnt usually poop out on you. I think most of the elites were falcons. Then there were the motherboards out of the arcades. some of them had internal memory 256mb, and 512. These were jaspers, and they rarely die... ever. haha. All of the slims seem to be fine as long as you dont obstruct the airflow on the side of the box.
Personally as my stock box I have a zephyr. Its my second zephyr after the first one e74'd a couple years ago. Seems to be running well, I treat it well, but the fans and dvd tray keep getting louder and louder. Seems to be on its way out.
My second xbox, which is my modded one for homebrew and such is a glossy slim (trinity) and it runs flawlessly. It does run hotter at the processor than the other boxes(homebrew temp monitoring), but that is to be expected with an integrated cpu/gpu.
