If you're able to slide and hold the car sideways no problem with an open, a j30 will be fine for you. It will drive a lot smoother in turns and nicer for a daily. It will lock up and do its job, but obviously not as aggressive as a real LSD. And obviously not as predictable as a welded.
If you're the type of driver who finds it impossible to drift with an open, then just get a welded since the car will basically drift itself. With a j30 its not going to kick out instantly no matter what like a welded will. You have to do it a certain way, but if you know how, it will be fine
If you want your rear end to lock up but still keep it a nice daily then go with a j30. If you want something super predictable and easy as hell to slide and dont care about the down side then go with the welded.
For a j30, try not to buy one off someone's 240sx cause it will probably be toast. Try to get one straight from a j30 with low ish miles. Try to find one 6 bolt (95-97 i think), so you dont have to swap the axles, and if you decide you'd rather have a welded, all you have to do is swap the diff again
hope that helped