I like predone cropping because you can't really crop a full screen ratio wallpaper to fit widescreen unless the wallpaper being cropped is hella big (like, bigger than 1440x900). It's way hard for me to find (good) widescreen wallpapers these days. I'm not saying a zip for like...ten different sizes, but maybe a big size for widescreen AND fullscreen, and not just full screen.
I prefer to download multiple versions of one of the same wallpaper and also make uploads this way. A 1600x1200 image for example doesn't look that great if the screen resolution is for example 1024x768, in the past I had to resize such wallpapers myself to make it look right, well it's not a big deal to do that. Also if somebody has a logo or name in the wallpaper then it's not clearly visible.
In the last time I have two packages, one normal sized and one widescreen, and people can DL for the resolution they use. Dual screens also in two version normal and widescreen, the same with triple monitor version.
I like the max resolution you want to give out, running a dual screen 24" widescreen thats a total res of 3840*1200 and I have to compensate for the 150 pixels in between so that the wallpaper doesnt visually jump.
So in fact I need wallpapers of 3990x1200 almost impossible to find and I always need to edit them. So Im definetly in favor of max res.
the artist making the cropping/resizing has control over composition and image quality. the latter is especially true if a wp has a resolution of something like 1600x1200 and the screen is 1280x1024 because the downsampling and aspect ratio changing while stretching the wp to fit the screen makes for an ugly sight.
I think wp's in multiple seizes is 1. A nice touch to all the viewers and 2. many screen resolutions isn't cropped down good for, some looses details and some get more etc etc.
I voted for several resolutions. That's what I prefer personally anwyays. It's like 10 mins more work outside the XXX-hours you've already spent on the piece so I reckin' it's no big deal for the artist