It's hard to go wrong with any race engine these days. They all make great power, albeit different from one another. I currently have a few race engines....Alpha Orange Head in my Truggy, Alpha Green Head in my Buggy, and a Go Tech (Rex Welsh Modded) B21 as a spare....all 3 engines RIP very well for MY driving style.
That's really the kicker with any engine you select. Will it work for YOU. Not will it work for the fastest guy at your track....or can Adam Drake make it go really really fast...can YOU make it go really really fast is the real question. We have a few locals that LOVE the RB WS7 III engine.....I bought one for my Truggy, and while it runs AWESOME...the power does not suit my style very well in a Truggy. It has little to no bottom end....and it SCREAMS on the top end. So I can drive it, but I struggle to make certain jumps since my corner speed is not up where it needs to be to drive this engine correctly.
That doesn't mean the engine sucks....it has GREAT power, just not where *I* want it....
So if you are teetering back and forth....drive one. Find a local that has the engine you are debating...and take it for some laps to see how it feels. I love my Alpha Orange Head in my Truggy, but others have tried it and it's too explosive on the bottom for them. I find it perfect for me....and with 4 gallons on it now...it still has a TON of pinch left to it. I easily expect another 4 gallons from this little inexpensive engine, and the internals do NOT look "cheap" to me.
Anyway...just my .02 cents.