His best performances came in the 2012 tour to India when the team was clearly in a transitional mode and had lost/started losing most of its top players, and the new guys were yet to settle in.
Not to **** on the guy, he did his best and it is indeed a respectable average vs India (did very well on the 2008 tour too, was hopeless in 2011 in England) but it wasn't quite the same team.
I thought he was an excellent player, but saying he's better than Ashwin is a big call. Saying he's an all conditions bowler is also a big one too (he was pretty handy), but clearly he wasn't that great vs the best teams around at the time. If he did pick up wickets, he was expensive.
I know he doesn't get the benefit of playing ~50% of his matches on home pitches, though, so I do cut him some slack there. Just saying, he wasn't better than Ashwin that's all.
I think people are shortchanging Swann a bit. The reason I rate him highly is his matchwinning ability which is not reflected by raw numbers. He was much better than his numbers show.
From 2009 to 2013, in most series, Swann would produce a matchwinning spell. Any spinner who can consistently win you a match a series, home and away, gets more credit to me then one who does a holding job and averages less.
In 2009, Swann averaged 31 in South Africa, but won England a crucial test in Durban.
In 2010, Swann didn't do much in the series but did seal a victory with a fifer against Australia in Adelaide on a batting wicket, something Ashwin has yet to do in SENA.
In 2011, in England against India, in the series you said he was hopeless, he still sealed a victory with 9 wickets in the last test.
In 2012, Swann won matches in both Sri Lanka and India was good in the UAE.
Plenty of other matches won by him in between and after.
Swann didn't end up with the prettiest figures but he was a tremendous asset for England and one of the big reasons for them going to no.1. His job was to win matches when the pacers couldnt and he did it well.
Ashwin is pretty much a matchwinner in the subcontinent and West Indies thus far in his career. Yes, he improved tremendously in Australia this time around, but I dont expect him running through sides outside of spinning conditions. But to make clear, due to Ashwin's sheer wicket output overall, I think its fair to rank him higher.