i use both, modo and blender.

blender has a lot more animation features and other things modo lacks like a modifier stack, a compositor,...

blender doesn't support ngon modeling yet but they are working on it. this was the main reason i got modo. i originally come from maya and can't get used to the quad limitation for most modeling tasks.

modo has a better renderer (though the blender renderer can do some things the modo renderer can't do) and the painting tools are better too. the blender painting tools will be improved during project apricot i think.

the sculpting performance is about the same for me but modo sculpting works a bit differently. it's image based and during sculpting you can enable a bump mapping shader so it looks as if you are working with more polygons than there actually are.

modo still lacks a 64bit version.