Everything is been said already, everybody got to make good points.
I'd just like to add a few things:
Regarding the original question, games look the same whether you load them from USB, Disc or SD card.
The video output of the Wii has nothing to do with the way games are loaded into the system.
Now specifically for the Wii, I would get component cables ( or whatever equivalent they have in Europe now, SCART, or RGB I don't know what is called anymore ) regardless of the type of display you choose.
Component are always better, not only will colors be better ( less bleeding ) but also it's the only way to enable progressive scan mode, on both GC and Wii games.
Without component cables , you are stuck with 480i, the Wii will refuse to output 480p.
Now with that out of the way, CRT vs LCD :
If you can find a old fashioned widescreen CRT TV, 32"+ ( my father has one of those ) then enable progressive mode, I believe that's the best you can do with the Wii.
Games will look good, naturally antiliased from the TV scanlines, and VC games will look as close as the real thing as it gets.
If you decide to get an LCD HD TV, I would say 22" is perfect.
If you get a larger TV, the bigger it goes, the worse will the Wii look, even with component, I promise you that ( I tried myself ).
I was actually trying to get a 22" LCD myself, one that goes to 720p at the most.
Remember, 1080p on such a small device is pointless, and the more the device has to upscale the Wii, the worse it will look.
If there was anything out there with a native 480p resolution and widescreen ( and probably cheap as dirt ) then I'm sure the Wii would look best on it !
So big screen, stick with CRT.
Up to 22", the Wii will look great as well ( not so for VC games though ).
Me, I'm waiting for the Wii U, then I'll get a 47" or something, and enjoy my HD Wii !