If there is a good Rotax Max Challenge series nearby, then I would pick the Rotax. If the nearest series is TaG, I wouldn’t pick the Rotax, as it’s been rendered uncompetitive by SKUSA when they added a 20lbs penalty this year. The Rotax is relatively competitive if the track has a lot of mid-range but will get killed if the track has lot of point and squirt turns.
I’ve run Leopards, Motori and Rotax and the Rotax is by far the more reliable engine. In fact, right now, they are offering a 12 month warranty. I don’t believe that any other engine supplier even offers a one day warranty, I think that says a lot about reliability and robustness of the package.
Like Dan said, it’s easier on the drive train because of the lower RPM, chains and sprocket seem to last forever. I think the lower RPM contributes to the longevity of the motor, you can go 2 seasons on the bottom and 1 season on the top.
With the advent of the new generation clutch, the package is unbeatable for reliability It’s not the sexiest sounding or looking motor but very utilitarian and damn it’s nice when the starter work every time. Get a powered kart stand and you can go to the track without need for help.
The carb is not complicated, just find someone or a shop that knows what they are doing and have them set it up for the track you are running. The carb is very forgiving once set up right, especially if you run the same track.