If your not into shifting gears you should consider a direct drive hub motor.
I live in hilly country and have had no problem with my hub motor I am also running 52 volt battery. My bike started out as a very basic cheap mountain bike. No issues and bike handles fine at 60kph so most bikes can be converted with no issues.
Unless you plan on super gnarly off road riding direct drive works well. Less stress on drivetrain, ebrake capable means less wear on mechanical brakes while increasing range by 5% and if the chain breaks you still have motor to get you home. Good Luck