I take one. My diet isn't really bad, but I don't eat a lot of fruit or veggies..so I supplement my diet. I think depending on your goals, the multi may not be a waste regardless of your diet. Certainly after a hard workout, the vitamins and minerals will be put to use...
I take Controlled Labs Orange Triad. It's a great MultiV, plus joint support, and digestion support as well. The ingredients are also well sourced. And you can get 15% off the normal price of $30 for 45 days at the M&S store.
What kind of training do you do?