I flew both aircraft. The 175 is much more comfortable from a cabin perspective. It's tall, seats are wide, and as others said, "feels" as big mainline aircraft. There are no bad seats. The CRJ-900 is longer and narrow. You may have to duck your head when you board. That said, turbulence was a little more of a concern on the 175, especially when sitting in the back. Our flight attendant's always asked us to be more strict with the seatbelt sign after I switched the 175. If you can get a seat near the wing or toward the front on either plane, you'll feel less turbulence. Honestly, if you're a nervous flyer, I'd shoot for the 175.