The first thing that struck me about these bikes was how similar they are. Neither of them are lightweights; if you're looking for a fast, light bike, you should probably look elsewhere. Both of them have very stable handling. And both of them eat road bumps as well as any bike I've ever ridden.
On that last point: I've ridden some bikes that seem to transfer every bump to the undercarriage of the rider; many of those were light, fast bikes. And I've ridden heavier bikes that seem to do the same thing. I've also ridden bikes that were designed with wide shock-absorbing tires to keep vibrations away from the rider; my Kona Big Rove AL is a good example of this.
But with both the Straggler and the Vaya 2, it seems that the frames eat most of the vibrations. Both of them use fairly wide tires (42mm and 41mm respectively), but I have ridden other contemporary bikes with wider tires that did not do half as good a job of keeping road vibration away from the rider. This leads me to believe that the frames of these bikes play a huge part in keeping the rider comfortable.
As for the differences:
The drivetrains are totally different. The Vaya 2 runs a Shimano 105 groupset with a road triple. The Straggler runs a groupset that is mostly SRAM Apex; the cassette is from Microshift.
Despite the fact that the Vaya 2 has a road triple and the Straggler has a compact crankset, I found the Straggler to be the better climber. I've always thought that triple cranksets allowed the rider to tackle climbs more easily; in this case, even though I was in the lowest gear on the crankset, I didn't find that to be true. However, most of the triples I've ridden before this have been mountain triples, so it may be my lack of experience with road triples that led me to believe this. But the relative ease of climbing with the Straggler led me to believe that the Straggler frame might be lighter, despite the reputation that Surly has for producing heavy frames.
Note: The copy on the Vaya 2 from the Salsa website claims that it's drivetrain is compatible with "any road compact or touring triple crankset." I'd love to put a different triple crankset on the Vaya 2 and see how that affects its ability to climb easily.
I believe that the Vaya 2 might have more braze-ons. Not quite sure.
Could I make a choice between these two bikes? Not at this point. I would have to take both of them on far longer rides than the distances I was able to go today.
I'm also going to check out the 2017 Vaya Deore at some point; my current bike has Deore components in the drivetrain and I've been fairly impressed with them.