What is better for a 5’5" tall guy, a 20’ or 24’ trials uni.
For trials definitely a 20". And for a person 5’5", even more so.
David
If you were 6’2" I’d still suggest a 20"
24 feet eh?, send me a video of u doin trials on that beast 
hey, im 6’2". would that help in trials any?
Depends on what you were doing. For hopping high of course it would, it’s just a question of to what extent. Technique is the main factor though.
It just means a greater amount of manuverability. (spelling)
David
nearly every trials/street type trick would be easier on a 20 inch. lighter, smaller, bigger crank/wheel ration making it easier to roll out of tricks. harder to get speed, but you should be able to get plenty of speed anyway.