I began my moped career riding a supercub. i'd had others but that was the bike that won me
the fact of it's being most produced is pretty telling - it's the most demanded, it's the perfect fit, simple reliable inexpensive and very capable to fit many international markets, where being able to cheaply zip through tight city streets highlight it's accolades.
beyond that, look at almost every sub 150cc manual or semi-auto engine out there, they're all derivative of the cub and many are direct clones - the "lifan" engine power the vast majority of imported pitbikes and small atv's
I loved mine, I rode it almost 20000 miles myself having recieved it at 8k, all with relatively little maintenance, average speeds up to 40mph, easily transporting 2 people and a load of extra junk too, and at times pushing gas mileage over 150mpg. that's a badass motherfucker.
But the best? there can be no best overall. a wise frenchman once told me "the best wine is the wine you like best" The cub is my personal favorite vehicle, but if I could only have 1 vehicle forever, it lacks the speed, range and carrying capacity of a bigger bike. It can still shred offroad if you're willing to have some fun but it'll never perform like dedicated dirtbikes or enduros. It's a perfect fit for low cost inner city transportation but can't do much beyond it, or at least not as well as other options.
Still, if I put it one on one versus any other 2 wheeled vehicle, it's impact and influence and my personal adoration will put it in the winners slot every single time.
I also strongly disagree with the transmissions being a weak link, they're extraordinarily simple, the semi-automatic is very approachable and easily learned and enables one-handed riding, and it's very robust. theyre notoriously bulletproof motors. I've had cubs fail but any transmission issues have only ever been an issue on the cheap china clones