Board Thread:Warhammer 40k General Discussion/@comment-66.206.224.153-20131222032846/@comment-1302704-20140317030550

To answer the topic question,

Ultramarines are the most combat effective chapter. for no better reason then that they've got no true strengths or weaknesses, they're just the most well-rounded and good in most any situation.

If not them I'd argue the Minotaurs since they've got better gear then any other chapter except the Grey Knights, thing is they only ever deploy at chapter strength and thus you cant account for the standard company's strength so they're out.