Help- finishing w/ single crochet before or after

Hi! I am have knitted a vest. It is still in 2 pieces (front and back). I want to single crochet around the armholes and neck, but I am wondering if I should stitch top and sides of the vest together first and then go over it with the crochet - or if I should do the crochet first and then sew? I am such a newbie!!

I would put it together first, then crochet–the line of crochet will then be continuous and not interrupted by the seam.

Thanks very much - now I can get started on my finishing! :notworthy: :muah: