Piper Chuck has this one put to bed (good answer Chuck
). The thing you need to realize is that model companys do the same as auto companys. They have thier LS's and SSR's and a whole host of jargon. You really don't need to know any of that. You need to know only a few. BB usually refers to ball bearing supported crank shafts. These engines are preffered. They usually have more power and are more reliable and longer lasting.
ABC is the other. ABC (or ABN) referres to the construction of the engine. The aluminum piston rides in a brass cylinder that is chromium (or in the case of n nickle) lining. They do this so that the piston to cylinder fit will be perfect when the engine is at operating temprature. Ringed engines are just like thier automotive counterparts. They use a piston ring (sometimes called a Dykes ring after the inventor) to make the seal at operating temprature. ABC engines are easier to break in and are generally easier to use for a beginner. Ringed engines are fine but take more to break in. You chould look at an ABC engine for your first one.
Most everything else you can disregard. I would not reccomend the OS LA series engines. Many like them, I do not. I have read so many threads and reports that were unfavourable to make me want to stay away from them. They do not have as much power as similar engines that cost the same.
Having said that. Here are some engines that I would suggest. I suggest a 45 or a 46 as they will be of use to you later on. I see no use for the 40's. The extra pwer will come in handy. Anyway the OS 46 AX, Enya 45, irvine 45, Thunder tiger 46 pro, and super tiger GS45 are all proven easy to use engines. The Thunder Tiger has a very devout following and is probably the best value of them.
One last thing I would point out. You are doing the right thing. Coming here and asking questions. If you have more try using the search function. It is right at the bottom of the page. Type in your questions and brows the answers. There is tons of info in here. Also check the engines forum. Lots of info there as well. Best of luck.
Mark Shuman