I am a 50cc fan through and through.
I was from the 80's era so pretty much the last of the 50cc school boys. My favorite bikes are the ones I rode at school, Honda Mini Trail, Suzuki RG 50, Yamaha RZ 50 and the Honda MBX 50 but I enjoy them all and have become especially fond of the earlier models even though they were before my time. There is nothing that can put a smile on your face like the ring a ding ding of that small 50cc motor reving at a million revs per second with the smell of two stroke oil.
Here are some of my favorite bikes.