I confess, I am a GG junkie. I have 4 of their packs: the Mariposa, the Mariposa Plus, Miniposa, and G5 Hyperlight packs. I like to show new and veteran hikers how to move to the “lite side”. :)
My recommendation would be to get the Mariposa Plus. The regular Mariposa is made of 30 denier 1.3 oz. silicone-coated ripstop nylon, whereas the Plus is made of 70 denier 2.2 oz. urethane-coated ripstop nylon. The difference in material amounts to the Plus weighing only a couple of ozs more, yet it can carry 5 lbs more weight. My Plus has survived a number of minor bushwacking trips into our local chaparral community.
I note that the Jam2 is made of Dyneema which IMO works better on long bushwacking trips. However, the ULA's Conduit is my pack choice for trips I know will involve bushwacking.
I have used both Mariposa models on 9-10 day Sierra Trips. A Ursack bear canister fits well in these packs. The 4 outer mesh compartments come in real handy for easy access to items or stuffing things on the fly, and carrying 1 - 3 liter hydration systems. A variety of 3/4 pads (NightLight™, Thermarest® 3/4 length Prolite 3 & 4, and Torsolite) fit well in the back support, and provide additional comfort.
I note that other responses in this Jam 2 vs Mariposa thread mention the Mariposa's larger volume (4200 vs 3000 cu. in.) and the nice hip belts to carry a heavy load comfortably. However, being a LW addict and following the slogan of “less is better”, I have reduced the amount and volume of my gear to fit into less cubic inches. For shorter trips, I now use the GG Miniposa.
As a final note, I like the fact that GG and ULA packs are made by two small companies run by two very nice and innovative human beings. They too each have an addiction for LW backpacking, provide great customer service, and attempt to stay on the cutting edge of this industry.