There is a long standing debate on whether the external frame backpack is better than the internal. I own both packs and have hiked many miles with each. Here’s a brief take on my experiences with them:
External Frame Packs
– are less expensive
– are lighter (with equivalent hip belt, shoulder pads, etc. on an internal)
– are cooler (since air can circulate between your body and the pack)
– are easier to pack (with specific compartments for your gear)
– are prone to snag on branches, vines, etc.
– are noiser
– are less trendy these days (which means there are fewer to choose from)
Internal Frame Packs
– are more expensive
– are heavier (with equivalent hip belt, shoulder pads, etc. to an external)
– are hotter (since they sit directly on your back)
– offer better mobility
– are generally more comfortable
– are harder to pack (since there are fewer compartments)
– are better in off-trail environments (with branches, vines, etc.)
– are quieter (since the frame is internal and less prone to squeak, etc.)
– are trendy these days (which means there are lots of options including some inexpensive 2 lb ultralight versions)
Generally, you will see more internal frames on the trail since more stores sell them and there are many more models from which to choose. Personally, I like the internals better and expect that most people feel the same way. Otherwise, you wouldn’t see so many of them on the trail. Hope this helps.