It's pretty important to not completely ignore the differences between Moss and Smoak in that conveniently selected two-year sample.
1. They both consist of a solid (~105 wRC+) and a crappy (~90 wRC+) season. Moss's solid season was the more recent one.
2. Moss has a track record. The 108 wRC+ Smoak posted in 2015 was essentially him at his best, while Moss had a 122 as recently as 2014.
3. In 2016, Moss posted the lowest BABIP of his career and it was 30 points below his career mark. Smoak posted the highest BABIP of his career and it was 30 points above his career mark.
4. Moss provides some versatility as a solid defensive OF and isn't a horrible baserunner.
Having said all that, I would prefer Pagan anyway.
1) Irrelevant unless you just want to pay solely for prior year performance, which is fair if a guy is 24, but not 34.
2) I have minimal interest in paying for Moss's 2012-2014. Dude has become nothing but an extreme boom or bust hitter over the past two years (see below)
3) Moss gets the Jose Bautista (aka extreme fly ball hitter) BABIP penalty because he's just a far inferior version of him now when hitting
- Moss had a higher average on hard hit contact in 2016 compared to 2015
- Moss had a higher average on fly balls in 2016 compared to 2015
- Moss had a lower average (a still very good .661) on line drives in 2016 compared to 2015 (.723)
Thus, the biggest change in BABIP? Moss had a 20% HR/FB in 2016 rate, and Moss hit .230 on 74 GB in 2016 against .267 on 105 GB in 2015. But Moss hits some of the weakest groundballs in the league, can't run and is shifted against rather heavily. Even .230, which is around the league average, is surprisingly high for Moss.
Unless Moss changes his contact profile (super unlikely for a 34 year old), a .260 BABIP will be around the norm for him. If he can keep putting 20% of his flyballs over the fence, he'll be a passable one trick pony power hitter. Once again, more than happy to let someone else pay for what is his absolute upside. Just because a guy is a flyball hitter doesn't mean he's good in the AL East. He still needs to be a...good hitter.
4) Moss is a medicore defensive outfielder whom I would not be against throwing out there for 120 games. This is his biggest advantage over Smoak.
Needless to say, I am not a fan of Moss. He was in my mind the single most overrated player in the FA class. I would also concur that Pagan is a significantly better option in LF for 2017, and also hopefully you wouldn't need to add a second year (mostly so if he sucks you can just cut bait and go to Pompey).