I have and use both.
For trail walking, I like the light weight, comfort and organization of an external frame. I have a Kelty, which is the lightest. I take it to scout camps, mostly. It replaced a Northface Back Magic, which I loved. Then I have a Dana Design external frame, which can carry the most weight. I take it hunting and when I'm packing trail maintenance gear.
Off trail, it's all about balance, and nothing balances like a well-fitting internal frame. I use a Dana Design pack, one of two depending on how much I need to pack. For a climbing expedition, it's a Terraplane. F