I'm still undecided. I believe Altuve & Judge are equally deserving
Each player contributes in their own way, as the two All-Stars play a different game. Judge plays the power game as a middle of the order run producer, leading the league in power numbers (HR, ISO, slg%) while Altuve is a speedy middle infielder with the rare speed/contact/power combo, leading the league in hits, AVG & runner-up in stolen bases. Of course, Altuve's power numbers aren't close to those of Aaron Judge but he's a two time 20/20 player nonetheless.
According to advanced metrics, Judge is a slightly better defensive outfielder than Altuve is a second baseman but since Altuve plays a more premium position than Judge, his defensive metrics are just barely better than Judge's (Altuve 0.7 dWAR/Judge 0.4 dWAR). We are all aware of Judge's strikeout numbers but both players are on-base machines with a similar OBP & Judge has the superior OPS, however Judge plays at the hitter friendly Yankee stadium which is a big contributing reason why. When adjusted to ballpark factors the two players have a nearly identical OPS+ (Altuve 167 OBP+/Judge 168 OPS+). On the flip side, if we want to get deeper into sabermetrics, Judge has a superior wRC+ (170) than Altuve (161). The metric wRC+ is a more polished version of OPS+ that is based on wOBA rather than OPS and similarly adjusts to ballpark factors.
As far as their individual value to the team goes, I believe both ball clubs would still make the postseason without them. At worst, the Yankess lose homefield advantage. The Astros take the division either way which is why I believe Judge has been slightly more important to his team than Altuve.
I'll wait until the final game of the season before voting but even when all stats are final I think my vote will still go to the player I have in mind.