Question for the cyclists...

I’m planning on ditching my well-aged mountain bike for a new one in the next couple of weeks (thankfully my company benefits package will reimburse a good portion of the cost ).

It seems that a 29in wheel size is the norm these days, although the 650b is also popular.

What do you all ride? Having never ridden one, why would I want a 29in vs. a 650b wheel size?

Inquiring minds want to know.