You can see the DL menu here: https://pc2c.mydeltamenu.com/BOS-SEA/
And B6 here: https://www.jetblue.com/magnoliapubl...n_W_LD_V01.pdf

This was Mint on BOS-SEA earlier in the year:


And DL F on the same route last month:


I think they each have their advantages/disadvantages:
B6
- More variety in terms of food choices
- Ice cream for dessert
- Better cocktails and an actual wine list

DL
- Better quality food (they use Do&Co for catering ex-BOS and the starter and some of the entrees are identical to what you'd get in D1 ex-BOS/DTW)
- Wider range of drinks (and Coke products)
- Premium snack basket (had like 4 passes of it on my flight) after the main meal service

Of note DL's preordering system seems to be broken for BOS-SEA/SFO so there is a risk you might not get your preferred entree, while I think on Mint they still load one of everything per passenger. So overall can't really go wrong with either option IMO