The only people who can say for sure who is the top 3rd character (after Tharg and Dredd) are the truly dedicated
2000 AD make so many series which start and end
For some It will be Slaine, Nikolai Dante (Long Run), Rogue Trooper (Long Run), Robo Hunter, The V.C.s, Kano & Bad Company, Strontium Dog (Long Run), Durham Red (Long Run), Nemesis The Warlock (Long Run), The A.B.C. Warriors (Long Run), Zenith (Long Run)
There are so many Thrilling characters and series which have appeard in the pages of 2000 AD from the fertile imagination of Pat Mills, John Wagner, Neil Gaiman, Alan Moore, Grant Morrison, Garth Ennis, Gerry Finley Day and Robbie Morrison.
Everyone will have their favorites (you can not have just 1... its impossible)
One of the reasons Judge Dredd totally stomps the vote is even if you don't like the character.... The World His Stories are set in has so much depth.
also
2000 AD really used to stretch the 'all likenesses to actual real life people and events is purely co-incidental' defense to the fullest (and break it) publishing brutal side splitting parodies (brutal as in you'll cry laughing, once you figure out exactly what they're doing and keep on laughing until it hurts to laugh any more, or you need a drink of water because you're so dehydrated) where Judge Dredd has more of an investigative role in the story.