It's kind of a tough call, IMHO. Personally, I tend to not like aluminum handled knives, because they tend to show wear much quicker/easier than G-10 scaled knives.
The Rift is a little lighter, a little shorter (Closed), with a little longer blade (& the blade's beefier).
The Presidio's handle might be grippier & more comfortable (The shape), & some people like a larger handle & more weight.
Admittedly, the different in weight & even blade/handle lengths aren't that big of a difference between the 2. In the looks department, that's too subjective. I'm sure there's plenty of people who like the looks of one over the other.
In the end, I think it boils down to comfort (520) or durability/wear (950). Personally, I've had the 950 & traded it, but I'm hoping to pick up an axis-auto (5300).
Good luck on whatever you choose.