Bob's Burgers almost certainly. Neither is my favorite. I think Family Guy is better at its best, but Bob's Burgers is consistently awesome. The two that come to mind are Awww Topsy and the new one with Bob's father 10 days ago. Honestly, I missed a lot of season 3 and 4 because I wasn't particularly inspired to keep up with Fox on Sundays, but I started again when Mulaney came out this year. I've probably seen about 50 episodes which should be a good enough sample at least.
Family Guy, on the other hand, hasn't had a really stellar episode since Season 9 which was a roller coaster. The Tea Party one was OK but just not quite as good as earlier stuff. Season 11 was just all around horrid - Bigfat, Road to Vegas and the retelling of the Christmas story were abysmal. I may have laughed one time combined on those. There were maybe 3 episodes that season that were even decent.
Also, Kristen Schaal is perfect. She makes Gravity Falls better than either. Yes, that's right, I actually like something on Disney Channel. Quite a bit too.
Oh yeah, great show. Hopefully Disney doesn't....Disneyfy it too much in the future.