Pariah

Hey, Ive trawled through a fair bit of the FAQ and such, so sorry ive missed the answers to my questions. I got a bit nostalgic after seeing the guy on Britains Got Talent, was watching some youtube video's and found this guy 50 years old and having a go at learning trials Fully inspired i decided it was time to get another bike. 20 vs 26, coming from a MTB background 26" seems to be whats suggested, but not having a bike on its back wheel for nearly 12 years would it be more sensible to start from scratch and get myself a 20"? furthermore I like the idea of a comp style of riding, but the majority of my local spots will be more street.... Stock or mod, I can probably scrape about £300 together for the bike, and for my money it seems that there are some nice second hand deals on Ebay and the like, but would i find it easier to get myself back in the saddle by buying brand new stock bike and beating it up myself? These things taken into account, any suggestions on a bike? Im not worried about looking cool as for the next 12 months ill be spending more time on the floor than on the bike, just for aslong as in your opinion it answers the questions above and can handle a battering im all ears. Cheers.