American League: Xander Bogaerts
National League: Asdrubal Cabrera
Technically, Asdrubal Cabrera is playing second base these days -- which he was initially none too pleased about -- but he might be warming to the idea given his 40.4% hard-hit rate and .408 xwOBA through 60 plate appearances since the change. On the season, he has a solid 34.9% hard-hit rate while striking out just 14.1% of the time, although he's hitting more ground balls (46.6% rate), so it's only translated to eight home runs. Still, he hit 23 last year, and posted a ground-ball rate below 40% the previous four seasons, so the power numbers could rise if he can keep up the hard contact and get back to hitting more fly balls.
Xander Bogaerts may have a modest 32.4% hard-hit rate, but like Cabrera, he could be on the upswing, with a 41.3% hard-hit rate over the last 30 days, and a 35.8% hard-hit rate since the start of May. Due to just a 27.7% fly-ball rate, Bogaerts' power numbers are sorely lacking this year, with only six round-trippers following a 2016 in which he hit 21. But even if the power doesn't fully return, he only strikes out at a 18.5% clip, and given his above average career BABIP, we can have confidence in his .303 batting average. It's worth noting that although Bogaerts has a ghastly .268 xwOBA, which is far lower than his .344 regular wOBA, there's evidence that speedier players can outperform their xwOBA, something he's done in each of the last two seasons.