A barrel roll IS more complex than an aileron roll! It is more difficult to learn, and more difficult to perform correctly.
If performed unloaded (0 to +0.5G) and started with sufficient nose-up attitude appropriate to the airplane's roll rate, an aileron roll is VERY unlikely to result in any overstress.
Either maneuver, done improperly, can result in excess nose-down attitude. In either maneuver, this is the most likely time the inexperienced pilot will panic and overstress the airplane. As OK465 indicated, it is MUCH more likely with a poorly executed barrel roll than with an aileron roll, since the barrel roll will normally result in a momentary 30-45 deg nose down when done properly. An aileron roll should not result in more than 5-20 deg nose down, again depending on the roll capability of the specific airplane.