if i was getting just one pack, it would probably be the metcalf.... that being said, for me personally, i like how my pop up rides on my body better, and love not having a frame sticking up unless i'm carrying a load.
from my experience with both, it would be a tough decision. the thing the metcalf has going for it is modularity.... if you aren't going to need a bigger bag in the future, the pop up is hard to beat.
of course you will get a lot of varying replies.... that's because we all have different needs, and different packs fit different body types. the pop up system has far exceeded my expectations of it. i have had some really heavy loads in mine and it's done really well.... pretty much, if i can get it secured to the pack, i can carry it.
a big bodied whole bone in buck is hard to secure into the pack (i have the 18) that seems to be the limiting factor for me, it lacks compression to lock in large bulky loads. i think if i had a couple meat bags for boned meat (longer thinner game bags) that were easier to get secured on the frame, it would haul more than i could. i tried to strap a roosie hame and front quarter to mine the first year i had it, and i couldn't get it secure where it wouldn't shift (lack of compression options) i just wanted to see how it handled the weight... a big ham from a big bull is no problem, an average size bone in buck is no problem, and i have made it work with a couple big bodied bucks bone in.... the weight was fine, it was just hard to lock it all into the frame.