The best hardtail bike and best full suspension bike for my cross-country riding needs, and in my price range and available to buy at local shops, came with 29" wheels and tires. I could have gone with a different bike company or paid to have new 27.5 wheels and tires but chose to stay with the 29" wheels. If I was a downhill racer it would have been a different matter.

It is a different selection pool for 27.5 versus 29 inch wheels. There are also more tire options at this point in time with 29 inch wheels.