“Both.”?
So you’re from Russia or China!
Well, Royal Navy also operated both types a while ago and US Navy leased one diesel from Sweden to find out that their ASW performance against diesel submarines is not so well off. US Navy should have known that earlier. ROKS submarines caused havoc several times during exercises: http://www.asiapacificdefencereporter.com/articles/244/SEA-1000-THE-LESSONS-OF-COLLINS
US Navy is still no way better today:
http://seefahrer.blog.de/2013/04/03/manoevertagebuch-westlant-deployment-28-29-15713453/
http://seefahrer.blog.de/2013/04/03/manoevertagebuch-westlant-deployment-30-15713582/
Microsoft Translator is available on these pages but a true Russian should speak German;-)
Music for diesel:
http://seefahrer.blog.de/2013/04/11/manoevertagebuch-westlant-deployment-07-08-15746059/
Russia or China? LOL
When you asked slow or fast I thought that you were referring to old, WWII diesel boats or fast attack nukes.
I qualified on an old, WWII diesel boat. ( We used to call them ‘slow ambush’. ) The day after qualifying I was immediately transferred to fast attack nukes. I have absolutley no idea why the Navy chose to do that, but they did. I do know that at the time my rating was ‘critical’ in that there weren’t enough of us in that rating. I got transferred around a lot.
All of the fast attack nukes that I rode have already been decommissioned.
Sorry for the confusion. ;-)