I take a generic multi-vitamin because I take a med for my guts that interferes with the fat-soluable vitamins, like A.
If you have diarrhea, take Caltrate 600 w/ vitamin D because calcium is naturally constipating. If you have C, it's generally best to avoid calcium because of the constipation problem. If you need calcium (ask your doctor), then look for one with a lot of magnesium in it, because the magnesium counteracts the constipation factor. Needless to say, people with D should not take magnesium unless told to by a doctor; it will make the D worse.