Gregory Juno 24L vs AER Go Pack

not a big deal. Plus, you want a snug fit with your gear as the load carries closer to your back, therefore more efficient at carrying the load..

These are going to be more suitable for ‘true’ one bagging (ie when you travel without a checked bag). If you decide to opt against a checked bag, perhaps look at a packable day bag and one of your options above, or take a look at the Peak Design Travel Bag, as this is designed with photographers in mind, is effectively a big bucket of a bag, and can expand from 35-45l (although I think when expanded to the full 45l it is slightly too big for most airlines). For a daily carry, you ideally want to be looking at something 25l or less, even under 20l.