Lots of opinions -- lots of experiences. My preference is for engines that don't give me grief, & also give good value for money.

If I don't pay much for an engine, I don't have high expectations from it -- and this is often born out in practice. For example, the cheap Tower Hobbies & GMS engines that I have purchased have given excellent power (as expected), but at the cost of indifferent tuning, fussier handling & potentially shorter lifetimes. I use them in throw-away applications. Same for Mecoa engines -- although I have been pleasantly surprised at their toughness.

My GMS .76 ringed engine is, so far, a pleasant surprise -- very cheap, good power & easy to tune. Lifetime is unknown, but being ringed, it should last a long time. I think that it is a good value.

Same positive experience with LEO engines, both .46 Pro & .61 Pro. They are cheap, have good, but not outstanding power, & are very tough -- a good value as well.

My recent experiences with OS engines have not been positive in the "go-for-dough" equation -- not enough performance to warrant the cost, plus spotty tuning & terrifyingly short lives. I sold all of my OS engines as a result of that unhappiness. Having said that, I just purchased an OS .46 LA (I don't believe I said that). I got it unused for $45 -- can't miss at that price & so far it has run beautifully (must be a good one).

In my personal experience, the absolutely shining examples of performance and value in the 40 - 46 sized engines have been the TT .46 Pro & TT .42 GP. I own five .46 Pros & two .42 GPs. All of them were very reasonably priced and all came out of the box running like oiled silk. For performance, the TT .46s have easily matched any .46 that I have owned, including the much-vaunted OS 46 FX & the "hot" GMS .47, but have been far better to tune & operate -- & so far have lasted & lasted, despite brutal treatment. The .42 GP is amazing in its power for a cheap bushing engine, outperforming an MDS .38 & matching an Enya SS .40 BB -- all with an APC 10-6 prop. It is much lighter than either one as well & uses noticeably less fuel than either the MDS, or Enya.

I also have a pair of TT .61s -- a GP & a Pro -- the plain-bearing GP matches the Pro for performance, but costs less & weighs less --another good go-for-dough choice.

I'm not married to any engine manufacturer -- just performance, value & easy handling.