ORIGINAL: Kansas Twister
I prefer the TT .46 Pro; mostly because the ST engines are butt ugly, heavy, and have a tendancy to lose mufflers in flight if you aren't careful about tightness. Having said that, the very cheap ($49.99) ST .40 makes a good trainer engine; but sell it or give it to a new flyer once you go to your second airplane.
I DO NOT recommend the Magnum .46; I've had three, one was so-so, the other two junk. It's funny, because their 4-strokes are very good for the money. Hey no offense, but this has been my experience and that's what I go by.
The O.S. .46 AX is an excellent engine, but too darned expensive for the minimal quality and performance difference over the TT Pro; $79.99 compared to $104.99 at Tower, that's a 31% difference...
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I like both the TT.46 Pro and the ST engines in that size range, but I have to agree that the TT is the prettier of the lot.
I have seen those butt-ugly GS40's stomp the grape juice out of some of the larger engines in that class range, so I wouldn't be too eager to sell it off if I had one that really ran good. Don't let the price fool you and don't load it down with a prop larger than a 10x5 or 6. This is a strong little engine.
(Old man slips into reminescing mode) It kind of reminds me a bit of my OS.32F-H that I owned and flew over a decade ago. Lots of .40's and .45's went home red-faced after coming up against that little monster. However, it was expensive. The ST GS-40 is not expensive, but runs like a scalded cat, once broken-in. Be patient and don't over prop it. After all, it IS a Super Tigre.