Between 2007, 2013, and 2018, I rank them as follows, from not as awesomely sweet to most sweet:
2007: as johnmd20 said, it proved 2004 wasn't a fluke, but there wasn't anything especially sweet about winning the pennant itself. Coming back from 3-1 was awesome, Josh Beckett was awesome, the JD grand slam in game 6 was awesome, the Indians botching their chance to tie it or take the lead (I forget) in game 7 was awesome, and the Pedroia home run to cap off the late blowout rally was awesome. Oh and the MFY losing to the Indians in the first round because of the Joba bug game was awesome. But it was less awesome than the others. Because...
2018: because it took getting through the 100 win MFY and the 103 win defending champs. Because Sale hasn't been Sale, because the bullpen has been so up and down. It's crazy to think they have gone 7-2 against these two teams given the state the Sox are in. That makes this pennant very satisfying, as does the aspect that it proves this 108 win team was no fluke and clearly the best team in the AL. But it wasn't better than 2013 because...
2013: because not only were they down 1 game to 0, they were down 5-1 in game 2, barely had any hits in the damn series to that point (seriously, they had 1 hit through the first 14 innings, and only 3 hits in 16 innings heading into the bottom of the 8th of game 2), but they were also facing that ridiculously talented and deep Detroit rotation. That series was ridiculously satisfying. The Lackey 1-0 win over Verlander in game 3. The nailbiter 4-3 win in game 5, with the Sox going up 4-0 and watching the Tigers eke out a few runs one by one until Craig Motherfuckin Breslow shut the door and then Koji went 5 outs for the save. And then of course the game 6 heroics, with the Jonny Gomes near home-run leadoff double in the 7th, the clutch Xander walk vs. Scherzer, the botched double play ball by Iglesias, and then the unforgettable Victorino grand slam on the 0-2 pitch. It was so, so satisfying to win that series and beat that Tigers team, without even considering the Boston Strong aspect.