"My wish is to buy a bag that will last me multiple trips that last between a couple of hours to a weekend away. "

If "A weekend away" means a weekend hike, carrying your sleeping bag, sleeping pad, tent, clothes and food for the weekend, aswell as some electronics and luxury items, I'd say you are way, way off with going for a 20-40l pack.
Unless you buy all your gear new (and thus can buy minimal, lightweight UL stuff), you will most likely have some stuff that are bulkier than other gear.

Me and my partner have bought ourselves new gear this year since we are planning hikes from weekend to week long hiking trips. We both ended up choosing the Osprey Exos and Eja, 38-48-58 litres packs that weigh 1,2-1,3 kg. We are very happy with our bags that carry weight phenomenally well, are really comfortable, have several good pockets and functions and are really multi-functional. Can't recommend them enough!

In addition, I have bought a Bergans 11 litres hip pack, that I use when we are out on dayhikes. It is an older model, but similar to Bergans Vengetind.