The Champions League is the ultimate test for European clubs, and before the start of this season's group stage, ESPN FC is looking back and asking you to decide which was the best of the 22 teams that won the tournament in the current era.

- Europe's best, from Marseille to Real Madrid

Starting Monday, our #UltimateUCL feature will ask you to vote as the champions go head-to-head, from Marseille in 1993 to Real Madrid in 2014.

Here is a look at how the contest will work:

Seedings

A panel of ESPN FC writers ranked the 22 Champions League winners, and those votes were collated into the following seedings:

#UltimateUCL seeds 1 Barcelona 2011 2 Barcelona 2009 3 Bayern Munich 2013

4 AC Milan 1994 5 Man Utd 1999 6 Ajax 1995 7 Juventus 1996

8 Man Utd 2008 9 Real Madrid 2002 10 Internazionale 2010

11 Real Madrid 2014 12 Barcelona 2006 13 Bayern Munich 2001

14 AC Milan 2007 15 Real Madrid 2000 16 AC Milan 2003

17 Borussia Dortmund 1997 18 Marseille 1993 19 Chelsea 2012

20 Porto 2004 21 Real Madrid 1998 22 Liverpool 2005

Format

In order to finalise the Round of 16 lineup, six play-in games are required, in which the lowest 12 seeds will compete against each other. The six winners will be placed alongside the top 10, and the matchups are as follows:

#UltimateUCL play-in games 11 Real Madrid 2014 vs. 22 Liverpool 2005

12 Barcelona 2006 vs. 21 Real Madrid 1998

13 Bayern Munich 2001 vs. 20 FC Porto 2004

14 AC Milan 2007 vs. 19 Chelsea 2012

15 Real Madrid 2000 vs. 18 Marseille 1993

16 AC Milan 2003 vs. 17 Borussia Dortmund 1997

After the Round of 16. the quarterfinals and semifinals will follow before the two remaining teams battle it out in the final.

Voting

For each round, voting begins at noon ET / 4 p.m. GMT and ends at 9 a.m ET / 1 p.m. GMT on the appointed day. Here is the round-by-round schedule by date:

#UltimateUCL voting dates and times Sept. 8-9: Play-in games

Sept. 10-11: Round of 16

Sept. 11-12: Quarterfinals

Sept. 12-14: Semifinals

Sept. 14-16: Final

So start thinking about the great teams you have watched over the years, and consider which of them is the best of the best.

You can also comment below or on Twitter, using the hashtag #UltimateUCL.