I currently have two packs that I use on long trips - a Granite Gear Nimbus Great Northern, which is an internal frame pack that is no longer in production, and what Ostrom now calls their Winisk II.  While the Granite Gear is certainly a good pack it pales by comparison to the Ostrom.  Ostrom packs are incredibly well built and are designed to fit and make heavy loads manageable.  They will last a lifetime of hard tripping.  However, as in most things, the best don't come cheap.  Here's the Ostrom site so you can see what the top end is and then make your choice of where you want to be on the price spectrum based on what is essential for you and what isn't.  One other thing about Ostrom packs is that, even though they are most definitely "modern" packs with adjustable, padded shoulder straps and hip belt and, in some cases, internal frames, they also include a tump line, which for me is a deal breaker.
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Though expensive I can definitely say that with Ostrom you do, indeed, get what you pay for.