bindings size up or down?
 

l will be getting a pair of k2 sonic binding, and it just so happens my boot size is 8. The Medium is something-8 while large is 8-11size. So do you think it would be better idea to get a large or a medium binding? what are some determining factor

i'd probably go smaller if you fit in the range...unless you have some chunky boots. it'll be less adjusting to strap in.

If you plan to keep the bindings, and you're still growing... maybe better to spring for the larger size.

Good advice. You might also look at whether the bindings are adjustable in size (eg heel cup can be moved to make a large binding smaller). If it can be and your boot fits decently in the bigger size, I'd go larger.

take your boots to the shop with you and see which size fits better.