Good question. Its unfortunate that you can't just ridem all. Do me this favor though, go to www.observedtrials.net, and ask your question there. Those guys are very well educated on several bikes, know the ins and outs, what they're specifically good for.
I bought a Planet-X Zebdi. Seems to be an okay bike. I think I'd prefer a Zoo or an Echo after riding for 10 months now. As for being a beginner, though, I've bashed the hell out of the zebdi and it holds up. You can also put a small travel fork on it to 'make the conversion' from huckin' to hopping. And you can goof around and at least entertain yourself doing some street riding when you are frustrated and can't make a move in trials.
my 2 cents.
Oh, BTW, you can buy trials bikes from the guys on the aforementioned site.