Back in the day, the boats that were a pain to track were the SS/SSKs, Nukuler boats were decidedly easier, but they have improved the radiated noise of the SSN/SSGN/SSBNs.... Still, the thing with subs is they are disruptive even when their presence is just unknown. Between nuke and fuel cell, I'd still go conventional, but it just doesn't have the same headline appeal to pollies. Aussie needs a substantial fleet of boats, either flavor, but numbers are needed IMHO.
Out in the boonies one day tracking a Victor-III (wiktor.. for trekkues...) our engineer in the center lounge chair spills his coffee pointing out an attack periscope of decidedly non-Russian plumage.... As the mission green had decidedly no friendly boats in the intel, we spent the next 3 hours pinging the stuffing out of the boat, along with passive tracking. Debriefing included a surprise visit by a pretty unhappy foreign military attache flown in at short notice, explaining the presence of their nuke. FWIW, it was definitely quieter than the "Wiktor" , which was pretty confused by the activity around his baffles. ASW/ISR had its moments.
"Dolphin 22"
(22. Submarines never cheat and rarely lie.)