Inspired by Tennis Channels controversial Top 100 list, I wonder what people here think are the most important aspects for a player to be rated. To make things easier, let's ignore the pre-Open Tennis period, I mean what's the value of winning 7 Wimbledons while being automatically qualified for the next final after each victory. Or how important is winning 10 GS during a period when the strongest players were absent? Worthless.
Grand Slam performances
Probably the most important aspect. Number of wins, finals and general performance in the 4 Slams. This is where players may be remembered the most.
Overall tournament performances
Overall number of wins and finals and also a breakdown between Slams, Masters titles, YEC's and performances on different surfaces.
Ranking
Another important aspect, what was the player's highest ranking, how many weeks at No. 1, year end No. 1's, weeks in the top 10, etc. This is also where players will be strongly remembered.
Doubles performances
This should only be thrown in as a "kicker", to complement your singles performances or to put some player over another one if other things being nearly equal (e.g. Bryans rule doubles but can't win crap in singles).
Head-to-Head
What was the competition like, did it include several other great players, winning record against said players etc.
Arbitraty stuff
Youngest ever, oldest ever, first ever, winning streaks, etc.
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Now comparing one criteria to another one can be tricky. For example how important is being No. 1 without winning a GS compared to winning a Slam but never being No. 1? How important is winning 2 Masters titles compared to reaching 1 GS final? Number of weeks at No. 1 compared to number of GS titles. And so on.