Wales centre Scott Williams believes the 2018 Six Nations has the potential to be the "toughest to date".
The 27-year-old scored the opening try as Wales' 2017 autumn campaign closed with a 24-22 win over South Africa.
Williams became one of only four Welshmen to have scored against the Springboks, New Zealand and Australia.
"All the teams are playing well at the moment. Scotland have especially shown the way that they want to play and we have as well," said Williams.
How the Six Nations teams fared in autumn
Scotland earned wide praise for the attacking threat as they lost to New Zealand before going on to trounce Australia 53-24.
Ex-All Blacks captain Sean Fitzpatrick described Gregor Townsend's side as one of the "major threats" for the 2019 Rugby World Cup.
Ireland also enjoyed a successful autumn, hammering the Springboks 38-3 before a narrow 23-20 win over Fiji with a 28-19 success against Argentina.
England's autumn included beating the Pumas before overpowering Australia and ending with an unconvincing win against Samoa.
France were less impressive, losing to New Zealand and South Africa before drawing with Japan, while Italy's only autumn win came against Fiji before defeats by Argentina and South Africa.
Wales began with defeat by the Wallabies, ground out a win against Georgia and again came off second best against the All Blacks before beating South Africa.
'Ruthless' All Blacks impressed Williams
The lasting impression of Wales' campaign for Williams - who joins Shane Williams, Alun Wyn Jones and Alex Cuthbert to score against the three southern hemisphere big guns - was the manner in which reigning world champions New Zealand secured a 30th successive win over them in Cardiff.
Williams, who will leave Scarlets for Ospreys at the end of this season, says Wales must rise to the All Blacks' "clinical" standards to build on the positive aspects of their more expansive style.
"They didn't create a lot of chances, but when they did, they scored them and that's where we've got to be - we've got to be ruthless," he said.
"We were comfortable first half and two mistakes in defence from first phase probably cost us the game and that's the difference in international rugby.
"We've got a lot of young guys and people coming in and they're just constantly learning now.
"They're only going to learn from what they've gone through in the last couple of weeks and they'll be coming back stronger."
Six Nations calls for Parkes & Navidi?
Williams' Scarlets and now Wales midfield partner Hadleigh Parkes scored twice on his debut, as Wales beat the Springboks for the third successive time in Cardiff.
Parkes now hopes he will make Wales' Six Nations squad, saying: "It would be an amazing experience to be involved in that."
Another hopeful for the tournament in which Wales kick off against Scotland in Cardiff on Saturday, 3 February is flanker Josh Navidi.
Injuries to British and Irish Lions back-rowers Sam Warburton, Justin Tipuric and Ross Moriarty helped give Navidi his chance to shine.
The Cardiff Blues back-row did so with outstanding displays against the Wallabies, All Blacks and Springboks.
"It was always in the back of my mind that I knew I could do it, but obviously you have to prove it on the park," said Navidi
"If you don't do that, talk means nothing.
"The closest thing I can compare it [Test rugby] to is derby games.
"The first game against Australia, I could say that the derby against the Scarlets the week before was harder, but it's gone up a step each week."