Currently? Air: planes will damage SS at a certain rate without any need for detection (like mines, basically, but those are forbidden in MP, AFAIK). You will still need roach DDs to screen your transports, of course (or route efficiency will plummet).
Going for naval-based ASW is not as effective due to extra research involved, and the fact that SS4s become virtually immune to Depth Charges with their low visibility. Of course, even SS4s can be hunted and killed, but it requires you to have CV (to do damage) accompanied with at least 5 dedicated (tier 3+) spotting cruisers - if you bother with all relevant Decisive Battle doctrine techs; will need more cruisers otherwise. So, if the end-result is virtually the same: why bother?