The Barclays Premier League champions were outplayed by the La Liga holders in the UEFA Champions League final at Wembley back in May which led many pundits in the media to declare the Catalans as the 'football team of the decade'.
However, Martinez reckons United are the better team but are just lacking a one-off result against Barca to prove it.
"In many ways they [Manchester United[ are better than Barcelona - that's just down to the mentality, the belief and they way they approach games," Martinez told talkSPORT.
"What Barca have is the way they play the game, they are very unique, you won't see another team in world football that will rely on 900 passes to win the game.
"The pattern of [Barca's] play is impossible to compare.
"But United have a blend and mentality in the squad that is the best in world football. It's just a matter of beating a team like Barca in a one-off game and see who can be European champions, as I believe they are on a different level than anyone else."
The signs are there that United are edging closer to achieving a result against Pep Guardiola's side. United recently beat Barca 2-1 in a pre-season friendly and are currently enjoying their best ever start to a league campaign under Sir Alex Ferguson with five straight wins.
Since United's 3-1 Wembley defeat to Barca in the Champions League showpiece, Ferguson has strengthened his squad with the sigings of Phil Jones, Ashley Young and David de Gea.
Last Sunday's 3-1 defeat of Chelsea also reinforced the view that the current crop of United players - including an in-form Wayne Rooney - are ready to challenge for the European Cup once again.
Barca for their part have also made great strides in the transfer market with Alexis Sanchez arriving from Udinese while Cesc Fabregas has made a red hot start in his return to his boyhood club.