Real Madrid are defending champions and Monaco the most "feisty" but Juventus goalkeeper Gianluigi Buffon says that Atletico Madrid are the "trickiest".
Buffon shut out Lionel Messi and Barcelona over two legs in the quarter-finals but his Juventus side must beat one of the above in the last four to keep alive his dreams of a first Champions League title.
On the eve of Friday's semi-final draw at UEFA headquarters in Nyon, Switzerland at 1000 GMT, all four teams were making the usual noises: there is nothing to choose between any of them, they say publicly.
But neutrals would probably prefer not to see a rerun of the 2014 and 2016 finals, when Real beat Atletico both times, in 2014 in extra time and last year on penalties in a tight and unremarkable affair that was quickly forgotten.
The 39-year-old Buffon said that Atletico, who would dearly love revenge over Real in the final in Cardiff, might have an edge over the other three teams because they are out of the La Liga title race so can rest players for Europe.
"The only distinction from the three teams is that Atletico Madrid have a more marked and defined position in the (league) standings," the stopper said.
"The other two (Real and Monaco) are fighting for the championship (as are Juventus) so that could be a factor."
Real Madrid, for whom Cristiano Ronaldo hit a hat-trick as they saw off Bayern Munich in the quarters, are favourites with British bookmakers.
But Juventus were hugely impressive in beating Barcelona 3-0 in the first leg and then holding the Spanish champions to a 0-0 draw at the Camp Nou on Wednesday in a defensive masterclass.
Italian media are confident that the perennial Serie A winners can deliver Buffon Champions League glory at last.
Gazzetta dello Sport cited strong evidence in Juve's almost "impenetrable defence" and Gazzetta columnist Alessandro De Calo wrote of the prospect of domestic and European domination for the Turin club: "Henceforth, there's no doubt: there's a smell of the treble in the air."
Beaten Barcelona defender Gerard Pique concurred, tipping Juventus to lift the trophy they last won in 1996.
"Over the two legs they were better than us so they deserve to go through to the semi-finals. I think they can win the Champions League this season," Pique said.
French league leaders Monaco remain outsiders but they have already claimed victims in Borussia Dortmund in the quarter-finals and Manchester City and Tottenham Hotspur before that.
The French side are full of attacking vim and have hit a staggering 141 goals in all competitions this season.
And in teenage striking sensation Kylian Mbappe, allied with a rejuvenated Radamel Falcao, they have the firepower to trouble even Juventus and Buffon.
The Champions League final is on June 3.