An OS 46fx or Thunder Tiger 46Pro would serve you well for both years and models to come. They're both ABC-type ball-bearing engines that have a reputation for user-friendliness and good power. I've got a 46fx that is a sweetheart of an engine, and a couple of Thunder Tigers that I've been nothing but pleased with. It's hard to go wrong with either of them. The main difference is cost and needle valve location. The Thunder Tiger is a lot less expensive, and the OS has the needle vavle further from the prop. What that means is that when you go to make adjustments to the engine your fingers won't have to come as close to the spinning prop. If you're mindful of what you're doing it won't matter much.

ABC and ringed are the two methods engines can use to generate compression in the cyclinder. Aluminum, Brass, Chrome (ABC) uses the different thermodynamic qualities of the metals to achieve compression through piston fit. Ringed engines use a compression ring around the piston. For all intents and purposes you won't notice much difference between the two anymore, and the majority of sport engines are ABC-type.

The other big difference is ball-bearing vs. bushing supported crank shafts. BB engines have noticeably higher performance, but a bit higher weight. OS's LA series is a bushing engine, as is Thunder Tiger's GP series. They cost less, but you get considerably less performance. The other side of the coin is that these engines tend to last a long time.