Swann was absolutely brilliant in the recent SL series. I don't know when was the last time that an English spinner was able to produce such turn and bounce and make the batsmen so uncomfortable in SL! He's a very clever bowler too but I don't know how he would do if he wasn't backed up by such a competent English Test team - their fast bowlers are in peak form now and they have some decent fielders too.
At one point in time, it was reckoned that Ajmal was unplayable but it is clear that is not the case. He is still very effective though, in both attacking and defending and has more variations than Swann, so I may pick him in an ODI team over Swann.
Narine is the new hot commodity in the spin bowling market. Batsmen still look like deer caught in headlights when trying to read him. As others have said, let's see if he goes the same way as Mendis.
Afridi is also an incredibly effective ODI and T20 bowler. I think he would get selected in quite a few teams over better spinners because of the combination of attacking spin bowling, fielding and (hit or miss) batting.