I agree with John B. It's all a matter of personal preference. I bought an OS 46 LA *trying to save money* and ended up having to replace it because the engine simply cannot pull as hard as the OS 46 FX (or comparable). I currently run two Tower Hobbies .46 ABC BB and I love them. I have read that thee engines are difficult to tune (my first one was because I bought it used without manuals) but I got it broken-in and tuned quite nicely.

Good luck to you !