This post was going to be Best Young Adult Novel of 2015, but since Stand-Off is the only YA novel I read in 2015, I didn't think that would be fair. So Best Sequel it is, then.
Stand-Off might not be amazing on its own, but when paired with the first book, Winger, the two novels shine brightly. Winger was a much more somber piece, and Stand-Off is the exact opposite. Side by side, the two books compliment each other brilliantly. Andrew Smith could have very well drifted in the same direction, but he fought the obvious and wrote a followup devoid of formula.
This is the second year in a row that Andrew Smith has made my "Best of" list. If you've never read an Andrew Smith book, I suggest starting with Winger or Grasshopper Jungle. This author is damn good at what he does.