speedracerntrixie gives excellent advice. I'm currently using an LT-40 with an HB engine as a club trainer for instructing. Excellent combination.

If you want recent/brand new, also consider a OS .46 (https://www.horizonhobby.com/product.../OSMG0548.html)
OS has always been noted as being a bit overpriced, but their main line models (not economy) are very good to excellent. And being a current model, if parts are needed they are more available.

If you do get one early, read up a lot on proper break-in. And the process is different for one with a piston ring vs. one with an "ABC" piston/sleeve. It can be all too common for a new owner to run the engine too lean (or even too rich for an ABC version) in the early stages, which can at worst damage it so that it never runs correctly. In either event, count on having to run several tanks of fuel through it on the ground, before it is ready for flight. More for a ringed engine, fewer for an ABC.
Best advised to stay away from used engines, unless from someone that will work with you on it (like buying from a club member). Buying blind, you never know whether it is just used, or has been damaged through misuse.

Those of us with experience know well what to listen for when setting up an engine. Until you too learn, plan on buying a tachometer to assist in telling you where you are at in adjusting the needle valves, if going it alone.