internal vs external frame backpacks
Asking about internal and external frame backpacks is like asking:
chevy or ford
dodge or toyota
apples or oranges
iron man or spider man
There are pros and cons to every argument - some of it depends on what you like, and what your going to be doing with it. Personally, I do not think there is a "right" or "wrong" answer here. All I can do is tell you why I pick my packs and go from there.
Cool weather, day hike, cool weather overnight camping trip - frameless or internal frame. Having the pack right up against your body helps retain some of your body heat.
Hot weather hiking, overnight camping trip - Here in east Texas summer temps can get stay in the 90s, day and night. The external frame allows your body heat to escape from around your back. Just having that little bit of air space can help out a lot.
I have seen people carry an internal frame pack during the summer. When they drop the pack, their back and their pack is drenched with sweat. Just having that little space between your back and the pack can really help out when its 90+ degrees during the middle of July and August.
External frame packs feel stronger then internal frame packs - it might be just me, when I have a heavy load, I like having something solid to grab onto. Internal packs just seem flimsy and week - but I know that is not the case.
Military testing - the military test a lot of stuff. So there has to be a reason why they continue to pick an external frame pack over an internal frame. I do not know the "exact" reason, but there has to be something there.
Heavy loads - When you start dealing with heavy loads, the closer you have the pack to your body, the better. Extending the pack off your body just a few inches can put more strain one yourself.
Its like when you carry something that is heavy. Do you hold it at arms length, or do you get it as close to your chest as possible? The same goes for your back. The closer you hold it, the better it carries.
We can sit back and say - this pack does that well, while that pack does this well. But a lot of it boils down to which pack serves you the best. It might take you 3, 4, 5 or more packs before you get one that fits well and carries well. Regardless of what you buy, later on you might find something that you do not like.
My pack lineup:
Jansport cloth backpack
Medium alice
Large alice
Maxpedition Falcon-II pygmy
Maxpedition Condor-II
Maxpedition Vulture-II
MOLLE-II 3,000 cubic inch with external sleep system
Large MOLLE-II 4,000 cubic inches
Kelty Big Bend, 4,000 cubic inches
and a couple of others
All of the packs wear well and do what they are supposed to do.