Lot's of clubs in the area. Just join those that run the Trials for you. West Leeds Horsforth, Spen Valley, Huddersfield Falcons, Bradford, Yeadon Guiseley are all close and run Novice Beginner Trials to cut your teeth on. Barnsley, Eboracum, Ripon are a little further afield but again do some good Novice Beginner events. I'd use BUMPY to get some experience and confidence and then start doing the Novice Beginners in the New Year. Usually the first are at Deer Park Bingley and it depends which club that uses it gets their event in first.
As for the Bike. Either would do the job well. The Gasser has a lighter feel while the Beta feels more planted. It's all in which you feel more comfortable riding so getting out on them will tell you which is for you.