What is the best pack to buy?

I've always preferred hard frame/external frame backpacks

Osprey makes comfortable, durable packs. You're going to pay a bit more but you'll get all the bells and whistles. Literally mine has a plastic clip on the chest that is also a whistle. There's also clip inside to secure your car keys. I don't use it but it there's a pouch to hold a water bladder and an opening to can attach a tube that dangles by your mouth.

An outdoor outfitter like REI can help you pick out a pack that's suitable for what you'll use it for. Some are customizable, they can set it up for you. This is particularly important if you are looking at larger packs that carry a lot of weight

I'm happy with my ULA Catalyst as a one-size-fits-all pack, but I think that when it gets too shredded to repair I'm going to give external frame packs another try.

There are so many good options, and it really depends what you are looking for.

Are you looking to go ultralight and want a very minimal pack with few extra features, or do you want a bit more comfort/luxury features at the cost of some extra weight?

Do you want a pack for a couple days (lower volume, maybe <40L) or will you be carrying days worth of food etc. (maybe >50L)?

I tend to do 1-3 day trips, so my 38L osprey exos is just about perfect. lightweight, but not quite what most would consider "ultralight." but it has a few good, useful extra pockets and enough padding to be comfortable. I'm ok trading that bit of extra weight for those luxuries.

NO MATTER WHAT pack you choose, make sure you can try it on in person with full weight. If you have access to an outdoor store like REI in your area. If you ask, they should have weights to shove in the pack for you to try it. I cannot stress that enough, it is almost as important as trying on hiking shoes.