I havent played an end game sniper yet, but here is what i had in mind if i had one.
It really depends on what you intent to excel in with your sniper. Battlefield pvp or PvE dps?

Battlefield pvp - the obvious choice is all stat but if thats over your current budget i guess stamina cards + evasion cards will give you decent hp to survive.

PVE - agi cards mix with all stats, just maximize your dps potential