"What did you say you’ve got at home, Malfoy, a Comet Two Sixty? Comets look flashy, but they’re not in the same league as the Nimbus."
-- Ron Weasley (PS10)
Ron's comment that Comets only look "flashy" implies that they are no longer at the cutting edge of performance needed for a racing broom (PS10). Even Oliver Wood, when considering what broom Harry Potter should get when he joins the Gryffindor Quidditch team in Harry's first year, doesn't mention the Comet 260 as a possibility (PS9).
Lexicon list of Broom Manufacturers
From the Web
Harry Potter Wiki: