You can look at the 2-way contract in two different ways. One is as redundancy or the back up to the back up. In that case, you want the player that is the most ready but that may come with less potential ceiling.
The other way to look at it is to use the 2-ways on players that may be that diamond in the rough. More exploratory or developmental. These two approaches aren't necessarily mutually exclusive but they can be.
I like taking chances on guys like Tacko and Brodrick. If you get to the point where you are actually counting on your 2-way players to help the team, things have gotten pretty bad anyway.