Right lets sort you out buddy. You have Mod, 24" and stock. Mod - Small wheels - Rear 19" wheel, Front 20" wheel. 24" - 24" Wheels. Stock - Big Wheels - 26" Wheels Front and Rear. Wheelbases: Mod - Go from - about 1000mm - 1045mm. 24" - I am not sure on the wheelbase's of 24" frames. Stock - Go from around 1060mm - 1100mm. It is up to you really. You could ideally do with trying all the different types out first. If you are around the 6ft mark. I think personally you are going to be a little cramped on a short wheelbase mod, So ideally you would go for a long mod. If you think a mod is going to be too small for you. Get a 24" or a stock. The thing with 24" is. I have noticed that to be more street trials than actual trials. They are used more for bunny hoping and tap up's to bluntbacks etc. Where as with 26". People genrally ride proper hardcore street trials on them seeing as they feel comfy etc. If its possible for you, Just test each different bike and see what you think feels right for you. Hope you get yourself sorted dude. Dan.................. P.S - Anymore questions, Feel free to ask.