The Sage 1 and 3 are both are very well made knives with equal levels of fit and finish. Due to the shared design, they feel about the same as well and share the same tip up carry only deep ride wire clip. The only differences are the lock and the scale texture.
If you're left handed and tired of "making do" with right handed things, or if you're right handed and simply prefer the greater versatility of a hand neutral lock, then the Sage 3's bolt action lock would be a large plus in its favor. Otherwise they're pretty much equal in terms of strength and smoothness.
Then there's the scale material. Both now use textured CF laminates, but the Sage 1 uses a nubby "twill" textured CF that, IMHO, offers the optimal compromise between looks and grip. The Sage 3's CF has a more complex "cubic check" pattern that, while about equally effective in terms of grip, is considerably flashier looking. Too flashy for my taste, but if you're into argyle it may appeal to you.
Here's a photo of both, together...
FWIW, the Sage I is one of a rare few "wrong handed" knives I've ever even considered putting in my pocket, due to that twill CF, but then Spyderco came out with the Chaparral 1, which uses the same CF on knife with a thinner blade and a hand neutral midlock.