Gmail gas better junk filters. Being king of search sort of helps there, I'd think. Features it depends on how you use email, but gmail has way more features especially when you throw labs into the mix. If you use email primarily from mobile devices both are good. Hotmail has the edge on wp7 due to to do support, though.
The gmail web interface is less cluttered than hotmail and performs better, but I never use web interfaces personally. Maybe others do. Labels > folders.
IMO gmail only really shines when used with a client built for it. Like the Android gmail client.
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