Bit of a catch 22 question this mate
It really depends on your general fitness and musculature
I have been bocking for 3+ years now and I'm in the heavier ranges (110kg) and I find the 107 EXO's that I have perfect and can't bottom them
We did have a guy that cycled seriously visit us and have a go and he found that the muscles he had build cycling wern't much use (15 min and he was knackered)
Trampolining is the best sort of exercise so if you have a mate with a trampoline see if you can bounce on it for about 20 mins without being totally flaked
If you can go for the higher ones if not the lower
Wait for a few people in your weight range to answer though as they might have a different opinion
Jason