Any of the bikes you have mentioned will do the job, its more about which bike appeals to you the most, and about the level of local dealer support. You can also check the forums at
Trials Central to see other people's opinions about each bike. They all have their quirks and 'features', and you really need to try each one out to see which suits you best. Don't forget to adjust the controls before testing a bike to make things as comfortable for you as possible - a weird setup may colour your feelings towards the bike.
I would also try and figure out who has ridden each bike and how hard it has been ridden. Usually an expert rider will use more of the bikes potential, but at the same time give it a real hammering on much larger obstacles - so try and check how well the bike has been maintained and looked after. My current bike was ridden by a lower level rider who was extremely careful with it, and also was injured for most of the time that he had the bike, so it didn't get a lot of use or abuse (I ended up paying more for this particular bike than other similar bikes, but overall I am sure that it was worth it in this particular case).
Trials riders are extremely vocal and brand loyal so be warned about 'brand evangelists' - saying this an '02 or '03 Beta Rev3 would suit your needs perfectly :p
I'm quite excited as my brother has just got his '04 Beta, and I'm going to go and give him some 'guidance' on how to run it in. The main reason for making sure that he does it properly is that I hope to buy it off him when he gets his new bike next year. This also means that I'll have to help him as much as possible to improve his riding and limit the amount of scratches on 'my' new bike!!! He is an engineer and has bought the bike through his company so that he can develop some aftermarket parts for it - mainly to protect the muffler and water pump from crash damage. Because he is genetically related to me there is some urgency in getting these damage limiting parts on the bike as quickly as possible :joke: