Good set! All good. #1, #4 and #6 appealed to me most of all (especially #1 and #6, both of which I like a lot).
FWIW I'm not too bothered about centrality. In fact, I'd put it a bit stronger than that - Taking the backgrounds into account, I really like the composition of #1 and #4 just like they are and doubt they would be improved (to my eye) by decentring the subjects any more. I might be inclined to play with the framing of #6, pulling in the sides and top a bit (fractionally more off the right than the left), but that would leave it just as (or even more) central, which I think works fine.
Arguably #1 isn't central anyway.
Actually, now I look at it, I might make #2 even more central (and even taller/thinner than it is now).
I might take a slight amount off the left in #3 and the right in #5, #7 and #8, but such a small amount that I doubt anyone would notice a difference (except perhaps with #3).