Originally Posted by
solo79
Everything I have read says the Marlin has a good enough frame. Why wouldn't upgrading in the future be worthwhile?
Because it's an entry level bike, with a basic frame.
Being realistic, even if you put full XTR and CF parts on either of these bikes, you will still have and entry level bike as the frame will be holding it back.
Neither of these have tapered steerers, or thru axle front or rear hubs, without these, esp the steerer, the possibility of any upgrades is limited to impossible.
That said, both would make great starter bikes, if you like the sport would and wanted a better bike in the future, would look to sell complete and upgrade to a better bike at that time.