Hi Danny, I like 28s. 29s have drop centre rims and no compression release rod thru the tank, thats about the only difference from the first year. 1930 there were minor cosmetic changes ( headlight, hinged rear fender ) 31 has a different rear brake arrangment, , slightly different frame to suit, and styling changes to bars and headlight, as well as a slightly different oil pump. The motors are all the same, its really a matter of personal choice. I prefer the slightly cleaner antique  look of the pre 31s, some people prefer the "thirties more than twenties " look of the 31.

AT the end of the day, it is often a case of just getting hold of whatever year you can !

Thank you for your replies.  What is meant by drop centre rims ?

One small disadvantage to the 31 model is that the max. drive gear ratio is lower than previous years. This is due to the new internal rear brake drum arrangement. The drum has the sprocket riveted to it and I believe is 43 teeth. That's the smallest sprocket that will fit. The transmission sprocket size is limited by the chain guard, i believe 22 teeth is the max that will fit. The primary helical drive ratio is the same as 28-30. The end result is a much lower gear ratio that can't be changed. So top speed and highway cruising speed is reduced a fair bit unless you want to wind her up! By looking at the gear ratio tables in the 31 book, max high gear ratio for the 101 is 4.98/1 which is pretty low! The Chief and 4 both got the new rear wheel in 31 also. The Chief primary gear ratio was changed in 31 to reflect the larger rear sprocket, so it's still possible to get a final drive ratio of 4.21/1. The 4  is 3.94/1.  I think I can squeeze a 23 tooth sprocket into the chief primary, giving almost 4.0/1.

Anyway, all years of the 101 are good bikes!

Gene