I have the Sky-Tec XLT starter and BNC 60 amp internally regulated alternator on my O-360 with the short SJ cowl. It all fits and they have worked well. Enough so that if I were to build again, I would use them again.
The long cowl requires a prop extension even with a constant speed prop, double the length required for a FP prop, and is not recommended for acrobatics. (Although, a number of people still do some acro with the extension.)
"Best" is tough to pick, but there are good choices.
The B&C starter hangs lower than a Skytec NL inline. Both have a very good reputation, but the B&C doesn't leave as much room to be creative with a snorkel or airbox. The NL can also be configured internally so as to eliminate the firewall-mounted starter contactor.
The majority of new RV's seem to be getting an internally-regulated Plane Power alternator, mostly because it's dirt-simple to install. If you don't mind wiring the external regulator (or prefer one), B&C is the premium choice. If you are experimental-minded, know that a great many folks are happily flying various ND auto alternators.
