I had 6-8 students with the Evo engine this last season, and they have been darn good engines. Between the three you mentioned, I'd go with the Evo first. The OS engines are nice, and not at all a bad choice.

Lee1, the reason you don't see Evo and Futaba in the same mail order place is that they are distrubted by arch-enemies Great Planes and Hanger9. Most big online stores are closely affiliated with one or the other, but rarely both. TowerHobbies, for example, is owned by Great Planes, who import OS and Futaba. So it's no surprise their featured products have OS engines and Futaba radios. If you want both in the same place, you ususally have to go to the smaller LHS's out there, they are more likely to work with multiple distributors.