And now you're in the same dilemma as me!! The best quality stuff is mains powered. The battery powered options are either power hungry (Bass Buddy), noisy (Zoom), Crap (Vox), or have no compression (Bighead).
To be honest I make do with the Zoom B1on because I don't use it very often and when I do it's generally for playing along with something so the noise isn't an issue. It's also really light and the batteries last for ages especially with the screen light off. It's also mega cheap, so for £20 you really can't complain, it's amazing really.