Endless Mike
Sqirrel Girl fanboy
Superman is definitely faster than light. He's proven himself to be such many times. In the Lex 2000 special, he flew from Earth to Saturn in 4 minutes (Light takes 19 minutes to make that trip). He's flown faster than light to escape a black hole. He's fought Wonder Woman to the sun and back (as well as fighting her on the Earth a lot) in only 1 minute and 54 seconds (light takes 8 minutes to travel from the sun to Earth). He's fought Darkseid to the sun in the span of time it took them to say a few sentences. In Countdown, he flew from Vega (26 light - years from Earth) to Earth in a matter of minutes. In Infinite Crisis, he flew from Earth to Rao (in the Andromeda galaxy, millions of light - years away) in a matter of hours. He flew across the solar system in a few minutes to save Kyle Rayner. There are many more feats confirming this.
Compare this to Super Buu 3 (the second - strongest canon character in all of DBZ), when Vegeta arrived back on Earth. Baba said it was "far off" from Buu's position (which could be as close as a few hundred kilometers). Goku teleported there, and Buu sensed him and flew at top speed after him. However, Goku and Vegeta were able to have an entire conversation (Goku convincing him to fuse with him) before Buu arrived. Only a short time later, Dende arrived at the spot while carrying Mr. Satan, so it couldn't have been that far.
Superman is dozens of orders of magnitude faster than any DBZ character.