Tishomingo State Park is a good one! I'd recommend it. As I recall, the main campground is fairly small but its right on the water. I think they added some premium sites at a later time. There is plenty to do on Pickwick Lake. Lots of pretty scenery, good restaurants, etc. I've never stayed in the campground but we've used the boat ramp there many times. Nice park! If you decide to go, PM me. I can give you some good ideas of things in the area to check out.
We just got back from a 2-night stay (should have been 4-night, but got cut short due to weather). Tishomingo is a beautiful park! Lots of rock formations that you don't see anywhere else in Mississippi. We stayed in campsite #14, which is probably the best one in the park. It is fairly flat and has a large area of land between the road/pad and the lake. It is about 80 yds from the nearest restroom, and directly across from the worship center.
The lake is very low and apparently has been for a few years. I think I read somewhere online that the dam has a leak or something. Regardless, we didn't go to use the lake so it didn't bother us.
We didn't get to explore as much as we wanted due to weather, but there are lots of hiking trails and geocaches in the park. My boys enjoyed climbing on the Appalatian Mountain-type rock formations that we don't see here in central MS. We hiked on the Saddleback Ridge trail and part of the Outcroppings trail. There is a neat swinging bridge that you can walk across Bear Creek on. In the summertime there are canoe trips you can float down Bear Creek on. There is also a swimming pool for summer entertainment and a very scenic disc golf course. There is a very neat area with an old CCC pond and dam with a trail around it, and a pioneer log cabin you can walk in.
We highly recommend this state park and would camp here again in a heartbeat.