ME25 is smaller and cheaper...but you probably already knew that. I have an ME25 and love it for quick and dirty direct recording - also performs adequately through an amp although digital distortion still isn't quite the real McCoy.
The big thing with the ME25 is, do you like the way it's set up? You basically have to set every patch separately and scroll through the numbers. There's no separate OD/Mod/Delay controls like a lot of Boss multi fx. Personally I love the simplicity of the ME25 but a lot of folks don't.
"Someone in the newspaper said that it was art." -Nick Lowe