I don't have any Tanaka experience except for riding a BladeZ with the Tanaka 33. Not enough power for my tastes but dead reliable.
I'm fond of the Zenoah/Chung Yang motors, the Zenoah is Japanese like the Tanaka but unlike the Tanaka there is no emissions controls. The CY's are Chinese clones but very close in quality to the Zenoah " maybe a little better plating/casting on the Zenoah "
The smallest one, the g230 is powerful enough to move a 200lb person up to 25+mph. The bigger bores " Zenoah G43 and CY460R can produce 45+mph in stock form. Add a pipe, upgrade the carburetion and do some port work and you have a bad a$$ powerplant!
The infamous Zenoah G62 is ungodly powerful and really expensive " $1000 for a motor that needs another $300/$600 in parts in order to run it with a clutch and pullstart.