I've found that I can get by in most situations with a long sink-tip (24-30ft). I fish in waters that are 20-30ft deep fairly often, but rarely if ever do I find myself fishing right along the bottom in those depths. Most of the fish I catch in those depths are either suspended or relating to some sort of cover such as drowned timber or brush piles or rock humps which means I don't usually have to get all the way to the bottom and stay there. I'm not a big fan of casting full sinking lines, but having said that, I do own one that I use in those rare case when I have to get all the way down there. It's just usually my last resort.