It depends on which model and total volume vs hydration volume. When you say 2-3L, those are totally different packs. When you filter, make sure you think about 2L of water vs 2L total. If you mean 2-3L of water, then you want the pack with a 3L bladder. I tend to prefer just water in the bladder, so I also carry a bottle with Maurten in it for fuel. This might reduce the size water you need in the pack.
Also, will you want it to hold a spare tube, toolkit, pump, food, etc? If so, get the ones with the external pack attached. If not, you can fit a few small items like your id, a credit card and phone in the ones with no attachment.
I’d also recommend spending the extra to get the quick release hose attachment.