I can't say as to which are the best, I bought my set from eBay . Seller was holiday123 (now known as Winterholiday) I am very pleased with this set. I know that, Kenny Kong (?) makes a set and they are supposed to be really nice. You may have to check around on how to contact him.
I ran mine yesterday, to break in the gearboxes and they show no sign of strain. More than enough power to turn them. I would imagine that, it depends on how much you intend on running it and for how long in a time period.