I suggest you spend a fair amount of time reading the information on this site, both stuff on the first page and many of the threads before spending any money. First and foremost, you want a pack that fits you well - that could be any of several brands.

The external vs internal debate is interesting. A lot depends upon the type of trips you will undertake. Externals do fine on trails, while internals and frameless really shine off trail and in rough country. Externals are the only way if you will be packing staggering loads, but you seem like a sane person.

I would recommend that you borrow or rent (think REI) and try them out on the trail before making a purchase, and buy from a place that will give you good expert fitting. Don't be afraid to spend money on this item, if necessary. Backpack,boots, and sleeping bag are three essential items that will affect your enjoyment and well being on every trip. They are key items. You can easily scrimp and save money on other stuff.

You will probably always have use for a well fitted, internal frame pack with about 3500-4000 cu in capacity. A quality one will last forever. Just be sure it fits.