We generally use the hydrated salts whenever there's an option. The anyhydrous salts would work fine, but over time, if  the salt is hygroscopic, it could absorb water from the air. At that point, you can't really be certain what proportion of your solid is actually water, and then you can't accurately weigh it. Of course, just because you get the hydrated form, in principle, there's no reason that it won't absorb even more water. Some chemicals absorb so much water (even in air-conditioned environments) that they can dissolve themselves completely (deliquescence).

If only the anhydrous form is available, then it's probably not very hygroscopic. There's no easy way to know in advance. Even the MSDS sheets aren't too informative about this - for instance, the MSDS for calcium nitrate at JT Baker doesn't say anything about it being hygroscopic, even though it's deliquescent.

Your best bet at this point is possibly to post a list of what you were thinking of buying and have someone here on the forums check it over. (I'm hoping to address this issue over at the wiki. I would like people to list metal precursors that work well for pipetting, inkjetting, or both. It's still in the baby stages, but check it out: http://thesharkproject.wikia.com/wiki/Recipes)

As a general rule, though, if it's available in both anhydrous and hydrated forms, then we go for hydrated salts. As with all chemicals, keep them in a temperature- and humidity-controlled environment with a tightly closed cap.