Trying to purchase a S6 capable of root.

I've been waiting quite a while to purchase my new S6 and now I think I've waited to long. Spending some time on the forum I've figured out the new firmware on the At&t versions of the s6 can not be rooted. I really want to purchase a phone I can root and put a de-bloated rom on. I spent some time on Ebay but the various version numbers just confused me and most posts didn't have the full version number listed. Would a certain version purchased on ebay, or a version with an unlocked bootloader, be a better purchase than taking my chances at the At&t store. Can anybody point me in the right direction?