Each one, when installed properly on undamaged pipe, work well, and do not leak. A slip-on spout relies on a setscrew to hold it in position, and that can dimple or score the pipe. Depending on the new one you choose, if that dimple or scratch ended up under the seal of the new one, it may be really hard to get it to seal. With threaded ones, it depends on the design. But, getting it to tighten up at the wall while being leak-free at the same time can be harder. Delta make one that sort of combines the two. You solder on their adapter, then screw the spout to it. Instead of the tapered pipe thread and pipe dope making the seal, it relies on a gasket seal in a similar manner as the slip on, but the adapter is solid, and soldered onto the pipe which can overcome minor scratches or a dimple.