They are all within 10% of each other in terms of power and torque. Reliability/quality is also very close assembler to assembler. This is because there are only 3-4 part manufacturers all working off the Honda Manufacturing prints. The assembly houses then buy the parts and put the motors together.
So, as long as you are buying from an assembler that builds in volume (successful), then buy according to price. Harbor Frieght will get to $129 fairly often, but you might hear about $99 ones at some locations due to inventory reduction, or liquidation of previous models. Lots of people sell these engines.
There is a good market for upgrades on the 196cc clone engines that are the 6.5HP models.
Russ Barrow
Russell ATV