I'm on window's 7 and totally new to the android world (switched from jailbroken iphone), but I've tried Double Twist, Winamp, Music WithMe, and iSyncr...
I like Double Twist Player's interface on my phone, but it was slow as hell to sync via wifi.
Winamp I've always found to be a resource hog so I wasn't a fan of that whole setup.
Music WithMe is absolute crap, had to link my facebook account with it and it would randomly start downloading music (I'm on the 2Gb a month plan with At&t and I'm already hitting 1.5Gb a month as is...) and eat up my data.
iSyncr is great, but I'm not a fan of the original Android Music player as I listen to podcasts and they end up just getting thrown in with my regular music...
Anyone out there come up with a solution that fixes most all of these issues?