I've used both extensively. The kifaru frame is beefier but more uncomfortable and doesn't move with your body nearly as well. Plus, it's much hotter on my back. The Exo is far more comfortable and unless you are carrying more than 150lbs, I'm not sure the load carry differences are all that much between the two. More than 150lbs, I'd probably opt for the kifaru but I'd pay a price.
I've never been crazy about Kifaru bags. They are somehow too simple but too complicated at the same time. You are forced to buy a base bag and then find some kind of configuration for lids, pockets, pouches, straps, bottle holders, etc. The PALS webbing on the belt is nice but, IMO, not as versatile as a plain strap ie Exo or Kuiu (esp for pistol holsters or bear spray holsters).
Anyone else notice that the new "Reckoning" bag is basically a straight rip off of Exo's bags minus the stretchy large back pocket? Kifaru saw that Exo's bag was selling due to it's design and simplicity. If you like kifaru's frame and bags but Exo's simplicity then maybe this is your solution. Packs are very very personal as far as fit and need usage so trying as many as possible (with weight) is the only way to know.