I reckon these are the best:
Indian Wells (128 draw, big stadium, full crowd)
Miami (Same as above)
Rome (The premier clay court MS event)
Cinncinati (Always seems to have full capacity crowd, which is really important at an event which is supposed to be prestegious. I hate the WTA events which have sparsely populated crowds, it's embarrasing for the sport. At the WTA YEC last year, there was only about five people watching, they must have been giving the tickets away. Actually, as much as I dislike the guy, I reckon they should give the WTA YEC to that Texan matress person, who will put some money into it. But they shouldn't play it outdoors because it will just piss down).
Paris (It has more tradition than the other indoor MS).
I reckon these are the crappest:
Monaco (No-one bothers turning up as shown last year, when Spadea was the only one who could be bothered, Federer and Hewitt couldn't and Agassi hasn't shown up since '98. It also seems to get a bit cold).
Hamburg (This is purely a money-making exercise and it is too close to the FO whch explains why few can be bothered to turn up)
Canada (Last year they opened the new tennis centre for the Tornonto event, which put it on a par with the Montreal site, but there were still empty seats which is bad)
Madrid (If you're thinking of ways to reduce the schedule at the end of the year, then this one should be scrapped, or made to alterante every year with Paris. Although it is better here than in Stuttgart, when it was normal for no-one to be watching in the crowd, and Sampras and Agassi to pull out without any reason)