One could argue that Discovery is dirtier than Astana/Liberty Seguros/ONCE, but one could be easily proven wrong when presented with a few simple facts. For instance, Discovery/US Postal has NEVER had a doping positive. You can forget about the supposed 6 positives from 1999. That 'testing' has been thorough and comprehensively discredited. Astana/LS/ONCE has had many doping positives (Heras, Ribiero, Nozal) and their team manager was caught red-handed in the initial Puerto sting. People think Discovery is dirty because they hear it over and over and over again from the french press. You would be hard pressed to find any team in the last 20 years that has managed to steer clear of doping scandals. Yet, because they win, they're dirty.
Merckx was a great rider, but comparing him to people competing today isn't fair. "Merckx raced a lot more and won a lot more races than Armstrong" they all say in unison. Pity they never continue that thought and recognize that Merckx's competition raced just as much if not more than he did! Also, many of his less successful competitors actually had regular jobs because cycling paid even worse back then. Back then the Tour was not so much more important than all other races. Riders didn't focus their entire season on doing well in that race. If you want to win the Tour today (by far the most important race in the world), you don't disadvantage yourself competing in every race during the season. Merckx was always the team leader and the team always worked for the sole aim of Eddy winning. Armstrong was less imperious preferring to work for his teammates in races he wasn't focussed on. Merckx raced against Belgians, Dutch, Italian, French, WEST German and Spanish cyclinst. Today's peloton comes from a much broader talent pool. To win today, you not only need to beat the old cycling countries, but Russians, the old Soviet block nations, Americans, Canadians, Columbians, Scandanavians, etc. There are a lot more good riders today. The doping drugs of today are also much more effective than in Merckx's era. Cycling is so vastly different today than 35 years ago that deciding who's the best ever is nearly pointless.