I can confirm that the smaller overhead bins on the A side will *just* accommodate my Tom Bihn Western Flyer (commuter jet "full size") SOFT sided carry on travel pack. The maker lists its dimensions as 17.9" (w) x 12" (h) x 7.1" (d) (That's a 26 L/1600 cu. inch bag.) Only a malleable bag with these dimensions will fit!

I can put the Western Flyer in the smaller, A-side bins on an AS regional jet, but I do have to push and squish a little to shut it. (Or the FA does as we prepare to take off.) On the other hand, I frequently get the entire bin to myself as almost every passenger has a rolling case they *must* put on the other side.

Like most solo travelers, I like the A side better, but I wouldn't switch if I had the bulkhead. I find reaching the overhead difficult on larger aircraft (painful or impossible due to a frozen shoulder), but they aren't so high on the 175. Also, these flights are short enough that I can make do with just my Kindle or phone in hand, whereas I'm in and out of my under seat bags many times on a multi-hour flight.