My local Kmart has been keeping both the Pal Plus and Zenith in stock for the most part (there are periods where they run out, but they get them back in pretty quickly). Others around here have reported the same. So I'd certainly check there first if you have any nearby.
IMO, the only things that make the Pal Plus preferable over the Zenith are the guide, and the event timers (which don't even always work right). Other than that, it doesn't compare in any way, and can act pretty strange and unpredictable at times. If you just want a "set it, sit back and enjoy it, and never have to worry about it" type of box, then the Zenith is it. The Pal really isn't. I certainly don't remember the Zenith ever shutting off in the middle of watching it the way the Pal has for me on occasion. And the picture quality doesn't even come close, IMO. I suppose if you're watching on a TV smaller than 27", that wouldn't matter so much, though. But at least in my case, you do give up a lot just for that guide.
I guess if you have two coupons to burn, it's no issue getting one of each. I basically did the same with the CM and the Pal - and I have a third one I'll most likely end up using on the Zenith, which I've already tried and liked a lot, before I even got my first coupons.
Like the above poster was saying, I've only heard mostly really good things about the Tivax (especially the PQ over composite - the online reviewers all seem to point that out, too), so I would certainly recommend that box, also. And of course, the Channel Master - which has the best PQ of all using s-video.