glow engines either have a ring around the piston or do not. the ones without a ring are labelled "ABC" or "ABN" (Aluminimum piston running in a Brass sleeve that is Chromed or Nickeled). Almost all of the modern engines are pretty good today, even the low cost ones like the OS LA series. Another cost factor is how many ball bearings are on the crankshaft. The lower cost engines have a brass bushing and the more expensive engines have two ball bearings to support the crank. Finally, the carburetors generally come with one needle valve and a air bleed (cheap) or two needle valves (more expensive).

I like the OS .46, the Thunder Tiger .46 Pro for beginners. The TT .46 pro is the best value, I believe.