Well they definitely are when rolled good. Reason is that STR can roll 300 with the usual affixes, but VIT only 200.
STR craft would roll max 330 str 200 vit, while VIT craft could do 300str 330 VIT.
The problem i'm having personally is to roll even close to high STR. So far from 56 crafts, the highest STR i rolled was 180.
If you are looking for a fast DPS upgrade, craft STR version. If you are looking for long term shoulders that are great in general (especially good for PvP), craft VIT till you get it right.