I would be sure to find reviews by gamers on anything that does upconversion, as those can introduce delays that don't affect anything passive (like watching a movie) but can be seriously detrimental to gaming.
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My own set up is... highly convoluted.
On the TV's end...
HDMI input 1 - Satellite receiver
HDMI input 2 - PS3
Component input 1 - XBox 360 (I got mine a couple months before HDMI output became standard on all models

)
Component input 2 - Wii / PS2 (universal cable, also has a 360 end, but I prefer to use the official cable. I have to switch off the PS2 in the back to keep it from interfering with the Wii's signal)
S-Video/Composite input 1 - Gamecube/N64/SNES (I have one S-video cable for these consoles, so I keep them on the same shelf and plug the cable into whichever one I want to use)
Composite input 2 (no S-video) - VCR/switchbox
Coaxial input - Famicom
The VCR's rear composite input goes to a switch box. I use the front input for plug-n-play stuff (Atari Flashback 3, Namco Ms. Pac-Man plug'n'play, etc)
Composite-only switch box:
Input 1 - NES
Input 2 - Genesis
Input 3 - Dreamcast
Input 4 - Unused
I do have an open VGA port on my TV, so I plan to (sooner or later) pick up a VGA box for my Dreamcast, at which point I can remove the switch box from the equation completely and just use the VCR's two inputs for the NES and Genesis (unplugging one or the other to plug in any plug'n'play stuff).
I'm probably losing some picture quality by going through the VCR and switchbox for those few systems, but I'm already not getting an optimal picture for them anyway by not using a CRT TV

So whatever