Citrates and lactates are salts of citric acid and lactic acid. Calcium citrate is best for people over 60, since many of them have reduced stomach acid, making absorption of common calcium carbonate less efficient. You'll also come across many claims for very expensive multimineral supplements through multilevel marketing. In general, be wary of these products. They are greatly overpriced, and the claims are unsubstantiated.
Vitamins are a different story.
The fat soluble vitamins E, D and K can't be absorbed unless you take them with a meal that has fat in it. Huge tablets of vitamin C and multivitamins may not dissolve very easily. Simply drop the tablet in question into six ounces of vinegar. For help figuring out which vitamins and minerals to take, click on the Vitamin Adviser for an individual recommendation. Let's chew, swallow and compare notes in the Boards.