Backpack recommendation to fit under airline seat

I carry an Osprey backpack that is very comfortable, plenty of room and easily fits under the seat. Note that it's more of a regular backpack, not one to pack a trip's worth of clothing.

I would ordinarily recommend going to REI and trying on backpacks, but it looks like the closest store for you is in Memphis. There are lots of good brands out there. Comfort is so subjective, but a good choice is to look at companies that make backpacks for hiking, like REI, Osprey, Gregory, Deuter. Sierra.com is a good place to find backpacks at discount prices, and they do carry a lot of brands. They generally have the measurements, as well, so be sure you know what size you're looking for. I would order several options and test each one out. Just make sure you can return them for free. I think Sierra and REI both allow that on most purchases. If you have store like REI in your area (EMS? Are they still around?), they should have weights you can put in the bag to approximate what you would be carrying in it, so know that when you go, too.

The size of a backpack to go under the seat in front of you varies by airline. What one allows another might think is too big.

Will this be your main bag or act as your personal item?

We flew Delta to Paris last year and upgraded to Premium Select. The way the seats were designed, we could barely slide the tip of our shoe under the seat in front of us. It was pretty surprising.

Sorry, not enough info.

What is your expectation? Is this a "daybag" or your only luggage for the trip? Are you trying to meet carry-on requirements for a specific airline, or a common denominator type bag that meets all requirements?

My general impression, is if you are looking for a backpack for all your packing needs, with decent straps and a waist belt, it will not fit under the seat. For use as a smaller daybag, then lots of bags would work, just depends on what you want to carry.