In electrical systems, the ideal maximum load that you put into the system is 50%. It is NOT recommended that you maximize the rated power capability.
Sa pagiging mas matipid sa kuryente, hindi naman nagkakalayo ang consumption (system loss) ng 150W and 350W. On no-load condition, mas matipid ang 150W, since mas maliit (mas kaunting components, mas maiksing windings, etc). But given na 112W yung load mo, masyado nang overworked ang 150W AVR. This is the reason na masyado na syang mainit. And yung init na yun, also consumes power. So in our case, you're better off using the 350W AVR. HIndi ibig sabhin na 350W sya, ay 350W lagi ang kakainin nya na power. It depends on your load.
This is like comparing a 1.3L car vs a 1.6L car. If lagi kayong puno sa sasakyan, or aakyat kayo ng Baguio, 1.6L its better. But on very traffic situations (naka-idle lang most of the time), mas matipid ang 1.3L.