Monroe Monotube reflex. I run them and they are awesome. I love the ride of my rig. I have the teraflex leveling kit as well, perfect setup for my rig.

 

Your springs are likely culprit for stiff ride. However, if you just want to try changing shocks, get adjustables. That way you can dial in the ride you desire for both road and trails. The Ranchos recommended above are a very good solution for a reasonable price. If you really want to go balls out and have ultimate adjustability, you could go for Kings, but they come at a price.