Which team has been the toughest challenge for the Heat in the playoffs so far?

Call me crazy, but I think the Philadelphia 76ers were our biggest challenge. Their record might not show it, but they match up so well with the Heat. They were young and fast, unlike the Celtics and Mavericks They also had multiple guys who can take over the scoring load (Holiday, Turner, Iguodala, and Williams), unlike the Bulls, who rely heavily on Rose offensively. The Sixers really gave the Heat a hard time in the first half with explosive starts. I also think Iggy is the best defender Lebron has faced in the playoffs.