Truth be told, I think a lot of us have gone through this.
I'm sure you'll get loads of conflicting advice but in my view, cruiser is worth a punt.
I love old school but I wanted to ride something more modern on the race track. So new school it was.
I love 20" but the masters are fast as (so are cruiser mind) but I plumped for cruiser to find my feet, with a view to one day trying 20" as well.
I think with cruiser I'll be able to do more and therefore get more out of it.
You can still do OS as well.