England forwards coach Graham Rowntree has highlighted the competition for places in the front row ahead of the Six Nations.
One of the most intriguing selection dilemmas head coach Stuart Lancaster has on his hands is at loosehead prop, where British & Irish Lion Mako Vunipola vies with burly Harlequin Joe Marler for the shirt.
Rowntree said: "We blooded Joe 18 months ago in that South Africa series. He very quickly looked the part of a trusted Test player.
"His form in the last six months has been exceptional. His all-round game has been superb. He's very, very accurate at the set-piece, but what he's offering outside the set-piece has really come on.
"Mako has come on leaps and bounds and the set-piece was a perceived weakness of his, but he's done a lot of work there. He's one of the best props in the world."
England's Six Nations campaign, which kicks off against France in Paris on Saturday, is expected to herald a new dawn for Lancaster's side with the likes of Jack Nowell, Johnny May, Luther Burrell and Anthony Watson set for debuts in the three-quarter line.
Such daring selections will provide hope for the other props in the squad as Matt Mullan and Henry Thomas await their chance to establish themselves for the Red Rose.
Lancaster is due to name his starting line-up on Thursday.