Which bag should I choose?

The 53 L is not a carry on. The 40 L will work fine. I have used mine on several two month trips. It is not a great backpack, meaning you don't want to walk long distances with it. it it works fine getting around town etc.

Best thing any traveler can do is go to Rick Steves' packing list, make a few mods and stick to one carry on bag and a big purse or a small backpack. If Rick can travel indefinitely with a carry on, so can anyone.

My parents were world travelers until about age 80, and I used to feel so sorry for my poor father lugging around her huge suitcase. My wife and I will continue to be perpetual travelers as long as we can each handle our own luggage. We're using Travel Pro 21" rollers that weigh 6 lbs. each.

Check the dimensions of the Farpoint 53L, if it's more than 21 X 14 X 9 inches then you will not be able to carry-on, if you plan to check it that it doesn't matter.

I am very happy with my Farpoint 40. It fits everything I need and leaves enough room for a few extras to come back with me. I find it to be comfortable to carry and it fits very nicely in the overhead bins on the planes. It doesn't become too heavy when full, I like the way it is divided up too. I highly recommend this bag.

Looks like the Farpoint 53 is over 22 inches high. If you don't pack it full, it might squish to 22 inches, but otherwise it won't be a carryon.

I have the Farpoint 55 and have used it for 2 trips to Europe. I love it and will use it for our trip next year. The 55 does not technically qualify as a carryon, but I have carried it on successfully. I just don't count on it. I wouldn't want to carry anything larger, and honestly it's not necessary if you are packing light. We are traveling for 6 weeks on our next trip and I'm confident the 55 will be great!