I had 4 of those listed, Axe Rossi, OS, RB and Sirio. Those not mentioned, sts and ninja. Right now I love the sirio power. Ive got 3, one has 2 gallons, another has one and I just broke the third one in. I cant say its going to out last the OS v spec, it made 10 gallons and is now a paper weight, but so far, sirio hands down.
The RB C5bb I had never did run right, come to find out the lower case has a crack in it (now a paper weight). The sts engine, it was cheap so I though I would try it out, never again (gave it awat). The ninja was great, smoooth power and never flamed (sold with hot bodies truggy). The axe rossi was a mamba (hot mod) it flat out screamed, busted a con rod after 6 gallons and it too is a papper weight.
Its hard to say this one is better than that one. Right now my sirios have me sold.

Werks Team Line .21 B7 Pro all the way. Cant say much about the others, but the Werks smokes my other engine(the V-Spec). Not knocking the V-spec, It has been awesome. The Werks is just a bottom to mid range beast.

Im a Go believer. My 3 port 'RTR' motor can hang with anything at my track. Even at bigger tracks I lose no ground to high-dollar engines. I just can't wait to get an actual RACE Go tech