Rule of thumb: use the vac passes unless you are specifically saving them for something else. Also consider that your 2018 allotment expires at the end of the year.

As a new-hire they really don't do much for priority since other, more senior, non-revs on vacation can also use them but they do waive the charges for F.

And speaking of F, list in F. You can always get a seat in Y while listed for F but not the opposite. It would suck to list in Y and see the airplane push without you with seats open in F.