vice grips, pliers, adjustable wrench are always a last option for me. so far, i haven't used them yet.
here is the order of how i use sockets. 6-pt, 12-pt, 12-pt spanner. i never really go down to the level of open ended wrenches.
what i do not have in my toolbox is a 6-pt spanner. i would prefer spanner + cheater over socket + breaker for one reason - the force applied is nearer the head of the bolt or nut. socket + breaker in terms of force would be better for long socket/bolt heads.
if you are going to use socket + breaker for shallow heads, be sure to push the pivot point forward.