Hey maddie,
I really loved the 38mm. Hand grip was absolutely amazing. I didn't do a whole lot of leg grip work when I had the chance because I was having too much fun turning 10 different spins into one big combo spin!!
However, some of the girls at Angel's did say that if you are just learning a more difficult leg grip required moves its best to learn on a 45 or 50mm. If you are more advanced, its not as much of a problem. But like anything else, you just get used to it, try, try, try again, and eventually you get it. No matter what size pole it is. Look at Bobbi and her girls, they do everything on those poles.
The best person to ask would be Angel, since the owns the 38. She could tell you first hand what moves prove to be more difficult. I know I am a little late seeing this thread, but I hope it helps.
I am a huge advocate for the 38mm. A smaller pole will spoil you rotten though. Fair warning!