im gonna kinda piggy back off you here. i like alice packs because they are damn near bullet proof and thats real important to me, without a pack that can handle the shit yer travelling is gonna be shit ya know. its a bummer hauling around a crummy pack, but my gripe with alice packs is you either gotta go with the external frame (which is a big negative for me since you cant make em fit where you need them to fit sometimes) or you go without a frame which just kills my back. so ideally ide want something with a solid internal frame and outside pockets like alice packs have because i like to keep my gear in a particular way which is a problem with alot of the hiking backpacks that are being made now by rei and other places. its just a big empty hole that if yer not filling it to full capacity you really feel that yer hauling a half empty pack around and i dont like that and im sure it leads alot of people to over packing because they bought a pack with 1 large main compartment and no smaller side pockets and what not. so outside pockets are ideal for me. gotta have a solid waist strap the chest strap not so much a big deal since i rarely use mine but its a nice option when yer load is heavy.
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@Hobo Mud i gotta give love for the external outside straps for a stuff sacked sleeping bag/mat. but overall i think durability is the most important thing for a good pack. ide much rather have a less comfortable pack that handled abuse over a really comfortable pack that the zipper busts out after a month. but ya know ideally ide love something that was at least somewhat water proof too. the most recent pack i got came with a rain cover that pulls out from the bottom and covers the entire pack, i havnt had a chance to test it yet but its a pretty neat feature. theres not much worse then bedding down for the night only to find half yer shit is soaking wet when you were only getting rained on for 15 minutes.