Ailerons will allow you to make sharper turns than a rudder-only plane will allow. It's not much more difficult to learn to fly with a fourth channel, and the extra control might even making manuvering to avoid obstacles seem easier.

You could take a look at the ParkFlyer RC BeginAir RTF or the upcoming Parkzone T-28 Trojan RTF, either would make an excellent first 4-channel aircraft.