The 28-year-old, who will skipper Wales against Austria at the Liberty Stadium next week, has shown himself more than capable of making the step up to the top flight with Swansea, with his leadership, reading of the game and strength making him one of the Welsh club's stand-out performers.
After a difficult start to this season, where uncharacteristic errors proved costly for club and country, the former Hednesford and Stockport man has bounced back to recapture his best form.
His defensive partnership with Chico Flores has seen Swansea secure clean sheets at Arsenal, Chelsea (twice) and Everton among others, and the Swans goals conceded tally of just 27 is the joint-third lowest in the top flight.
Wales coach Coleman, himself a defender during his playing days, believes his captain is right up there with the very best.
He said: "There is not a better centre-half in the Premier League.
"People may look at Ashley and see him playing for Swansea who, while they are a Premier League club, are not Chelsea or Manchester City, which may make it harder for him to stand out playing for a smaller club.
"But there has not been a better centre-half performance-wise over the last three months and I am not just saying that because he is captain of Wales."
Williams will get the chance to experience European football for the first time if Swansea can see off Bradford in the Capital One Cup final at Wembley on February 24.
Victory would hand the Swans a Europa League spot for next season, but Coleman believes the defender, who was linked with Liverpool and Arsenal during the January transfer window, would be a success in Europe's premier club competition.
He said: "Champions League football has the best sides with the best standards on the planet.
"It's hard because the tempo of the game changes quickly and you have to think quickly.
"But Ash is doing great and he has been doing very well, playing at the highest level."
Coleman, who was able to select Craig Bellamy in his squad for the first time since August, also rounded on Gareth Bale's critics following the Tottenham winger's brilliant goal in Wednesday night's 1-1 draw at Norwich, claiming it proves the 23-year-old is no diver.
"Someone tried to bring him down but he kept on going 50 metres from goal," Coleman said.
"He didn't go down when he could have and the player would have got a yellow.
"When he makes the decision to carry on going he doesn't know what's going to happen, whether he's going to put the ball in the net in three seconds.
"But he carried on and scored a great goal."