I would not add any VIT or INT on a softcore barbarian. They are more for brute strength, and frontline tankers.
Dex will add to your defense vs critical attacks as well as help aid your own critical attack, and Str will add to your damage.
Some people recommend going pure STR, and this can work especially if you are on a budget.
My advice? Try to get an even balance of STR/DEX (such as 80 DEX 100 STR, or 100 DEX 120 STR) but I would keep Dex around 100-120 MAX... after that you hit diminishing returns and it is better to stat STR.
This can be hard to hit without good +stat gear, so you may want to try the pure STR build, or get DEX ~70 then pump the rest to STR.