I think the Helix is kind of a risky choice. I know a couple people who have 'em and love 'em, and a couple people who didn't like them. (One just sold it after a few months.).

I have a Pod HD500, and there are some things it does well, but the dynamics just aren't there, and I couldn't get a usable tremolo out of it.

AxeFX 3 and Kemper have pretty great reputations.