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Pep Guardiola knows better than most how important Lionel Messi remains to Barcelona. If anyone knows a way of stopping the Argentine genius, it should be him. Isn't that right Pep?

Ah.

"There is not a system or coach to stop talent of Messi's magnitude," Pep said yesterday.

"The way he has been playing over the past four or five months, you cannot stop him. He is too good."

Messi, 27, scored twice in Barca's 8-0 win over Getafe on Saturday to reach 51 goals for the season, and in November became the Spanish league's all-time top scorer.

Pep Guardiola's Bayern Munich side are obviously special.

But even the most cynical mind would have to concede that at times, his Barcelona side were operating on a different level. Their 2011 Champions League victory at Wembley lives very, very high on my personal list of performances.

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But where does that side rank on the charts?

We've pulled together a shortlist of sides from the past 20 years and you can vote at the top of the screen. Please do.

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As well as casting your vote, let us know the reasons behind your decision, or let us know which teams we missed.

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Get in touch at #bbcfootball, external, pop on to the BBC Sport Facebook page, external or BBC Sport's Google+ area., external

You can also text us on 81111 in the UK only - don't forget to say who you are and where you are texting from.

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Bayern goalkeeper Manuel Neuer is widely regarded as the very best in the business, and he could well have to earn his corn over the next 180 minutes of this tie.

Bayern have conceded just 28 goals in all competitions this season - and are the only team in Champions League history to score six or more goals in three different matches of a single season.

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Germany manager Joachim Low is in the house checking out his numerous players on display.

He looks nearly as cool as Roy Hodgson.

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Bayern Munich suffered a 5-0 aggregate defeat by Real Madrid at this stage last season but have won five of their seven European Cup semi-finals against Spanish teams.

Who do you make favourites?

Andy West
European football writer

"Luis Enrique and Pep Guardiola have remained close, and when Guardiola was promoted from the club's B team to take over the senior squad in 2008, his replacement was none other than Enrique. They worked together for another three years, before Enrique departed for Roma.

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"After Barca defeated PSG in the last eight, Enrique reacted to the news that Bayern had thrashed Porto 7-4 on aggregate the same night with genuine delight, expressing his pleasure to see his old friend Guardiola safely through to the next round. Now they will go head to head as opposing managers for the first time.

"The boardroom reception will be somewhat frostier, however. Guardiola's deteriorating relationship with then-president Sandro Rosell was one of the reasons behind his 2012 exit, and he was also angered by comments from Rosell suggesting he did not spend enough time with his former assistant, the late Tito Vilanova, during the latter's cancer fight."

Read more from Andy on Pep's return here.

Nostalgia is a potent feeling in football; in life.

But for all the chat of Pep Guardiola and his influence on Barcelona, it shouldn't be forgotten that current coach Luis Enrique is having a brilliant first season in charge at the Nou Camp.

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Enrique - who played with Guardiola - said: "We aren't going into this as a game against Pep.

"He is the number one for what he has achieved and he's a friend, but this is such an important game for all Barca fans that it should be more important than any specific people.

"It's nice for the players to meet Guardiola again, but they know that this game is more important than just that.

"Guardiola knows most of our players but I don't think that will be decisive. There are many other factors."

Barcelona make one change from the side who put eight past Cordoba at the weekend. Marc-Andre ter Stegen comes in in goal. He only plays in the Champions League. Nice gig.

Barcelona: Ter Stegen, Pique, Rakitic, Busquets, Iniesta, Suárez, Messi, Neymar, Mascherano, Alba, Alves.

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It's just got to be a good game tonight hasn't it? Surely. I mean, look at how many good players are available.

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The use of protective masks has come on a bit since Gazza had to wear a ridiculous looking effort in 1993 for England, and expect Bayern striker Robert Lewandowski to wear this carbon fibre piece of kit tonight.

The Polish striker fractured his jaw and cheekbone in the cup defeat by Borussia Dortmund last week but he starts. Harder than a coffin nail.

Bundesliga champions Bayern Munich were able to rest their first-team at the weekend so make seven changes from the side beaten by Bayer Leverkusen. Robert Lewandowski starts with a broken jaw, he will wear a mask.

Bayern Munich: Neuer, Alonso, Benatia, Thiago, Lewandowski, Rafinha, Boateng, Bernat, Lahm, Muller, Schweinsteiger

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Four glorious seasons in charge, yielding a quite ridiculous 14 trophies.

From rookie coach to the most successful boss in Barca's history.

Pep Guardiola rewrote the rule book at the Nou Camp during his tenure from 2008 to 2012. He dominated Europe and bought 'tiki-taka' to the masses. Two Champions League titles and three La Liga crowns are living proof.

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Now, he's back with an equally dominant Bayern Munich side in the last four. He will be welcomed into the Nou Camp as a hero.

Will he leave as a villain?