Here's my take on your original question. I have all the engines mentioned except the OS .46LA and that is the one I recommend.

All of the engines mentioned are good. I have OS .46AXs in 2 twns (4 of them). They are the most reliable, easy to set engines around. I yanked other engines and bought these just to have the twin engine reliability.

My Thunder Tigers are down on power a little to my AXs, but they are old and worn. The TT .46 will probably do better on a small prop, while the AX will be better on a larger prop. Both are excellent engines, I just like the AX better.

I have had a Tower since they first came out, also a couple of GMS .47s. They run well, but are not as reliable as the OS. I have found that the Chinese engines take about a gallon of fuel to really get broken in well. Before that, they tend to not idle well, not transition well and not shut down on closing the throttle. I have seen guys drive themselves to total frustration trying to tune these characteristics out of a Chinese engine with low time. A few will do it, most won't. If you buy one, you may as well count on flying 12-15 tanks before all these areas come around.

The OS .46LA is less powerful, but most of the time you don't need all that power in a trainer, anyway. The .46LA will be plenty. It is very easy to start, run and set up. In a couple of tanks, 6 max, it'll be running great.

Another good thing about the OS .46LA is it has a plain bearing. I also fly seaplanes and a plain bearing engine doesn't have ball bearings to rust out. It's practically bullet proof for float flying. And trust me, your engine will get wel sooner or later. The .46, as compared to the .40LA, will have the little extra power you need for float flying.

If you want to go a little bigger, a sleeper, and best buy, in my opinion, in the .61 class is the OS .65LA. It turns many props faster than the more expensive .61FX, it's easy to run and you can dunk it, too, without rusting out a ball bearing.

Finally, when you get a second plane, most people with not too much experience, like to warm up on their old trainer for the first flight of the day, then fly the newer plane. Keep the .46LA in the trainer, even with floats, and get a new AX or Tower or TT for your next plane.