Who's the greatest?
Every so often, football has a habit of producing a truly remarkable team, a side that makes fans of all persuasions sit up and take notice and - perhaps begrudgingly - acknowledge them as something special.
It's a topic that could fill endless hours of nostalgia, discussion and argument: which is the greatest club side of all time?
With superstars like Lionel Messi, Xavi and Iniesta in their ranks, the current Barcelona side - who face Manchester United in a much-anticipated Champions League final - have been talked up as one contender for the title and BBC Radio 5 live's Monday Night Club will bring together a panel of experts to debate the issue on 23 May, five days before the clash at Wembley.
But are Pep Guardiola's side better than the Real Madrid team of Ferenc Puskas and Alfredo di Stefano in the 1960s, Johan Cruyff's Ajax side in the 1970s, the Liverpool of Kenny Dalglish in the 1980s, AC Milan's all-conquering 1990s outfit or the Arsenal Invincibles of 2003-2004?
Cruyff, Dalglish, Best, Maldini, Messi... all have claims to have played in the greatest club side ever
The Monday Night Club wants to know your take on the greatest club side of all time and they will use some of the comments from this blog on BBC Radio 5 live on Monday from 2100 BST as they attempt to come up with an answer to the question.
In no particular order, here's a list of 20 of the teams that should probably form part of the debate, but feel free to look outside the box and come up with a few of your own.
1. Barcelona, 1990s. Johan Cruyff's so-called 'Dream Team' won the Spanish title four years in a row and the club's first European Cup in 1992.
Stars: Ronald Koeman, Pep Guardiola, Michael Laudrup, Hristo Stoichkov.
2. Ajax, early 1970s. The team that gave the world Total Football, built by Rinus Michels and inspired by Cruyff, Ajax won the European Cup three times in a row from 1971-73.
Stars: Johan Cruyff, Ruud Krol, Johan Neeskens, Piet Keizer.
3. Liverpool, late 1970s. Champions of England in 1976, 1977 and 1979, Bob Paisley's Liverpool also won the European Cup in 1977 and 1978.
Stars: Ray Clemence, Alan Hansen, Graeme Souness, Kevin Keegan/Kenny Dalglish.
4. Celtic, 1967. Arguably the most remarkable team on the list, given that every single member of Jock Stein's European Cup winners was born within 30 miles of Glasgow.
Stars: Ronnie Simpson, Billy McNeil, Jimmy Johnstone, Bobby Lennox.
5. Manchester United, 1968. Ten years after the Munich Air Disaster, Sir Matt Busby had put together another superb United team that won the club's first European Cup.
Stars: Nobby Stiles, Bobby Charlton, George Best, Denis Law.
6. Arsenal, 2004. Arsene Wenger's 'Invincibles' became the first team in the modern era to go through a whole English league campaign without defeat.
Stars: Sol Campbell, Patrick Vieira, Dennis Bergkamp, Thierry Henry.
7. AC Milan, 1989/90. Arrigo Sacchi, with the help of Silvio Berlusconi's millions, created one of the most formidable teams in history. They were the last team to retain the European Cup.
Stars: Paolo Maldini, Franco Baresi, Ruud Gullit, Marco van Basten.
8. Bayern Munich, 1970s. The greatest German side, Bayern became the third club to win the European Cup three times in a row from 1974-76, and have only won one since.
Stars: Sepp Maier, Franz Beckenbauer, Uli Hoeness, Gerd Muller.
9. Real Madrid, 1950s/60s. Perhaps the team to which all others will always be compared. Won the first five European Cups and they played football way ahead of their time.
Stars: Francisco Gento, Raymond Kopa, Ferenc Puskas, Alfredo di Stefano.
10. Tottenham, 1960s. Under Bill Nicolson, they became the first English team in the 20th century to win the League and FA Cup Double in 1961 and won the European Cup Winners' Cup in 1963 too.
Stars: Danny Blanchflower, Cliff Jones, Bobby Smith, Jimmy Greaves.
Pele is regarded by many as the finest player of all time. Photo: Getty
11. Santos, 1960s. Won several domestic honours, were South American champions in 1962 and 1963 and won the Intercontinental Cup in both years too as they dominated world football.
Stars: Gilmar, Coutinho, Pepe, Pele.
12. Manchester United, 1999. Sir Alex Ferguson's greatest United side. The club's most successful season ended with a remarkable Premier League, FA Cup and Champions League Treble.
Stars: Peter Schmeichel, David Beckham, Roy Keane, Dwight Yorke.
13. Liverpool, 1980s. Joe Fagan led the club to European Cup finals in 1984 and 1985, before Kenny Dalglish's side won the League and FA Cup double in 1986.
Stars: Bruce Grobbelaar, Alan Hansen, Kenny Dalglish, Ian Rush.
14. Leeds United, 1960s and 70s. Don Revie's team may not have won too many friends, but they knew how to win - seven major trophies and never finishing out of the top four between 1965 and 1974.
Stars: Billy Bremner, Norman Hunter, Johnny Giles, Allan Clarke.
15. Barcelona, 2000s. Dutchman Frank Rijkaard transformed the Catalans, winning La Liga in 2005 and 2006 and the Champions League in 2006.
Stars: Carles Puyol, Deco, Ronaldinho, Eto'o.
16. Ajax, 1995. Louis van Gaal's team blended outrageous young talent with experience and they stunned Europe, beating a dominant AC Milan side in the Champions League final.
Stars: Frank Rijkaard, Clarence Seedorf, Edgar Davids, Patrick Kluivert.
17. Liverpool, 1990. Having lost the league title to Arsenal on the last day of the season in 1989, Kenny Dalglish's Reds responded in brutal fashion, cruising to an 18th title by nine points.
Stars: Alan Hansen, John Barnes, Peter Beardsley, Ian Rush.
18. Barcelona, 2009-present. Winners of a Treble in Pep Guardiola's first season in 2008-09, Barca won the title last season, again this season and are in the Champions League final once again.
Stars: Gerard Pique, Xavi, Andres Iniesta, Lionel Messi.
19. Inter Milan, 1960s. Helenio Herrera's team, based around the Catenaccio defensive formation, won Serie A in 1963, 1965 and 1966 and the European Cup in 1964 and 1965 too.
Stars: Giacinto Facchetti, Luis Suarez, Mario Corso, Sandro Mazzola.
20. Nottingham Forest, 1978-80. Brian Clough took the club out of the old Division Two, won the League in their first season after promotion and secured back-to-back European Cups to boot.
Stars: Peter Shilton, Kenny Burns, John Robertson, Trevor Francis.