I'm a huge fan of Comedy Central and the shows on there.  I've seen many comedians perform in stand up routines, shows, etc.  Out of all the comedians I've seen, the three I think that are the funniest are Carlos Mencia, George Lopez, and Dave Chappelle.  Here's some of the work they have done over the past few years.

Carlos Mencia:

• started out doing stand up early in his career
• one of his most recent stand up routines was No Strings Attached
• now has his own show (Mind of Mencia) that's now in his fourth season
• specializes in race jokes, ethnic jokes, and retard jokes

George Lopez:

• also began in stand up
• used to have his own show on ABC but got cancelled last year
• does stand up on Comedy Central and a recent stand up show was George Lopez: America's Mexican
• mostly does ethnic jokes, situational jokes, and jokes relating to himself and his life

Dave Chappelle:

• had his own show on Comedy Central (Chappelle Show)
• does stand up and did a routine just after he came back from Africa
• specializes in doing funny characters like Tyrone Biggums, does race jokes, and ethnic jokes

Each of these comedians have their strengths and talents.  For example, I like Carlos Mencia's impressions of stupid people and making fun of Americans' choices in their lives.  I like George Lopez's cleaner and more family style humor.  Also, I like Dave Chappelle's characters that he does and the special he had on his show which was Charlie Murphy's True Hollywood Stories.  Looking at these comics, it's hard to choose who really is the best.