To my knowledge, smokey black isn't one of the most collectable finishes, so bear that in mind if you're looking at this kit as an investment. Also consider that vistas are heavier than wood drums, so they're not the world's most practical drums if you're looking to gig them frequently without breaking your back.
That said: I love vistas. I had a set and still kick myself for letting them go. They're loud, resonant, and cool as hell.
The Slingies are a different story altogether. I've never played a Slingerland kit, but there are forum members who swear by them. (RogerSling, I'm looking at you.)
If it were me, I'd take the vistas, just because I already have two vintage wood kits (a 50s Gretsch and a 60s Club Date) and would love the variety. That's assuming the vistas are in great shape--pics would be needed.
Since you don't have another vintage kit, I think you need to identify a few things: first, are both kits well-priced? (Again, pics are needed for this.) Second, what kind of vintage vibe are you going for? If you seek a classic 60s vibe, the Slingies might be a better choice. But vistas have their own special kind of cool. Lastly, the vistas would give you a broader musical palette, since there are just more drums there. How much do you like big kits?
Lots to think about. Good luck!