http://www.sullivanproducts.com/StartersContent.htm

I don't have a "best" because I have only tried a few. I have the "Dynatron" it spins too fast with 24V and has too little toque at 12V. I actually snapped off the drive shaft on mine and had to repair it. When it gets slightly out of line at 4800 rpm things get exciting. I would look a the Megatron with the reduction drive.