I have a Thunder Tiger GP-61 on my Goldberg Protege .60 ARF, it's a match made in heaven! The TT Pro .61 has an excellent reputation, but I haven't flown one yet.

I have a Super Tigre G-61 Ringed engine on my Sig King Kobra. It's been easy to break in and tune, and a pleasure to fly. I keep hearing about folks who have problems with Super Tigre engines, I just haven't run into them yet. I own a G-51 and a Bull Ring .46 in addition to the G-61 ringed.

I'd buy and try the JBA .75 2-stroke before I'd buy the Tower Hobbies .75 2-stroke. I know a lot of pilots like the TH .75, but my experience with my JBA .56 has been really outstanding. The JBA .75 is only $99.95 plus s&h from B.J.'s Model Engines:

http://www.bj-model-engines.com/home.html

Still, the TH .75 is only $10 more before discounts, and it does have a great reputation. I think you'd be happy with either choice. The O.S. .65 LA has a very solid reputation, and is even reported to out-turn the .61 FX on several different props. I wouldn't hesitate to try that engine, either, particularly if weight is a concern.

As far as that goes, the new Magnum XLS .61 2-stroke has a very good reputation, and the Evolution .61 NT is also a very solid choice. Even the GMS .61 and .76 have a pretty solid reputation. I don't really think there is a bad choice in this size range.

Good luck, and good shopping!