1. Jeff Bagwell
This one is no debate, just look at his stats. Over his 15-year career with the Astros, he had an OPS of .948 a WAR of 79.9. That WAR value does not even come close to anyone else on this list.
He won the MVP award in 1994, finished second in MVP voting in 1999 and won Rookie of the Year in 1991. He won the Pennant with Biggio in 2005, before retiring at the end of the season due to back injuries. He would go on to be a Hall of Famer.