So I'm playing a 2h engineer solo on veteran difficulty and i want to know opinions on what would be better to put points in to- vit and str, or dex and str? Thanks.
The current best knowledge on the Runic forums is that vitality is only good for adding block to shields. The other things that vitality adds are HP and % bonus to armor. Both of those are useful but neither are cost-effective to obtain from vitality. You can easily get +HP gems that give you hundreds of vitality worth of extra HP. The way the game is balanced, beginning NG+ and into the late game, enemy damage scales up rapidly, far outpacing the amount of armor you will be able to get. This tends to make damage reduction and extra HP far more useful than armor. In fact, the later in the game you are, the more useless flat armor tends to become.
In summary, most of your points should be going into strength. Since you are using two-handed weapons, you will not have a shield, so vitality points would not be very helpful. You can throw a few into dex for both dodge and crit chance, but not too much. In Torchlight 2, the best defense is killing the mobs before they get a chance to land that one-hit-KO on you.