I was going through the same dilemma a month ago and I completely agree with what Steen said. If you look at the results of the CIK Winter Cup in Italy, just a week ago or so , there wasn’t a dominate engine. Vortex, TM, Modena, and Maxter all had good lap times.
You have to look at part availability, prices for replacement parts, and support. One might be a little better at smaller tracks and one a little better at long tracks but I wouldn’t expect one to dominate in all situations.