I have 3 oto's in my 55gal; they took care of all my brown algae in about 3 days. However, I have yet to see them work that diligently since, despite the return of some of the brown algae (but they do keep it down significantly.)
I also have several ghost shrimp. They do a wonderful job (although a little slow,) and they can reach some of the areas my oto's have a tendency to neglect.
All in all, I've been relatively happy with the shrimp and oto combination. I'd recommend either of them, depending on the tankmate plans or situation.