Closest, Coco Beach. But I agree with the others, not the nicest. Everyone seems to like Clearwater beach which is on the west coast but a little further away. Nice gulf coast beach. Unfortunately, and this is an opinion so take it for what it's worth, Florida east coast beaches don't get really nice until Palm Beach and points south. By nice I mean nice sand and pretty, clear blue green water. The gulf coast beaches and water are all very nice, soft sand (until you hit the shell beaches in the south around Ft. Myers) and gorgeous water.
Clearwater is very touristy, and can get very busy, especially on the weekends. Parking can be tough to find as well. I haven't been over there in a couple of years but they used to have public parking that you needed the "Parkmobile" app to pay for. Don't know if that's still in play. There is stuff to do there, restaurants, gift shops, beach type souvenir shops, etc. I guess if I were you, I'd drive the extra miles and go to Clearwater, but again it depends on what you're looking for. Either way, enjoy what Florida has to offer.