Those are ALL good engines, however the OS 30VG would be my least favorite out of all of them, I believe you can get a better engine for your money. The Axial .28 is a good, inexpensive engine, slightly more powerful than the K4.6. I haven't heard much about the Axial .32, but it should be a real powerplant. The Associated LRP Z.28R I've heard has tons of power, I think that would be a good choice also.

I haven't personally used any of these engines, I just know what I have read.