'Which pack' is too often asked [everywhere!] with no parameters set. It's like asking what 'reel' to get -with no line or rod weight established-much less 'water to be fished' described:-) ?! Simply doesn't 'work' that way.
Duration of trips, terrain [open trails or bushwhacking?] weather zone [hot, temperate, cold [wet?] winter, 'comfort level' of gear[quantity/quality-lightweight] that's acceptable for the USER and MONEY are needed to make honest appraisals.
Since FF in the Smokies is applicable here [assumed], then 'when' [winter packs have to be BIGGER-more Cubic Inches!], duration and whether on 'trailed' streams or bushwhacking for specs are the choices. Essentially you have to have your 'contents' BEFORE you can choose a suitable container [just as you need your FF line size BEFORE you choose the rod].
Thankfully this forum doesn't have to overcome 'tactikewl' military wannabe's that promote 6# glorified daypacks as 'essential' to toughness-but totally inadequate CI-wise.
Look to high volume ultralight packs of 4400ci and up to keep most contents inside. Oughta be in the 3-4# range MAX. The more you bushwhack the 'slicker' the pack should be [same as an ascending climbing pack]. Dyeema and kevlar /ripstop blended fabrics have supplanted heavy cordura in modern sport packs. If you like/prefer to 'tie stuff on' the outside and stay on developed trails, you can't beat a good old Kelty or packframe for versatility . BUT if you aren't hauling a duffel bag of gear, a 5gallon jerry can and/or an outboard motor, a newer UL internal frame is probably indicated:-). [The pic of Jim as an [overloaded!] child is a prime use for a pack frame [think bipedal mule 'packsaddle' concept:-)].
Being realistic, money is a big factor. The higher quality [lightweight] gear you can afford [AND how 'spartan' you can camp 'comfortability'-this isn't about a 'sickening ' elimination hike for SAS selection!] effects how many CI you will need in your pack. Personally I gave up on the 1 pr. of boots, 1 gun, and 1 pack that 'can do it all' decades ago-simply isn't optimal -unless you're a hobo[and he just suffers alot].
It's no simple decision because to be valid you need your 'contents' first. Simply using a siltarp rather than a tent eliminates AT LEAST a couple pounds and hundreds of CI. An 800 fill power 30 degree down bag is less than half as bulky and heavy as a synthetic.[BUT I don't use down bags in the smokies-simply too wet. Wet down is a killer just as is cotton in the cold. Now if you can sleep in JUST your denim bib overals, a canvas coat and brogans next to a fire -waking-up frozen to the ground like an old smokies bear hunter [Kephart], ignore my wussy recommendations:-)].
Personally I'm guilty of 'overspecialization' with a dozen packs, about 7 bags and 3 tents, 6 tarps, etc-THAT isn't necessary. It IS why you need the knowledge to get the 'right' contents to determine what size pack you need-AND get the most utility out of our worthless FRN's.
Again, it's comparable to matching fly sizes to water to be fished, the flies to tippets/leaders and line THEN the rod/reel. The pack is purely an accomodation that must fit your OTHER selections. Course, then you get into fit, comfort and color-all pretty personal by that point. [Why I have wool packs for winter still hunting-NO noisy nylon.] Just an example of thinking thru YOUR requirements.] Ghost