Wildcard teams have gone on to win the WS 6 times;

1997 - Florida/Miami
2002 - Anaheim/LA
2003 - Florida/Miami
2004 - Boston
2011 - St. Louis
2014 - San Francisco

Washington has strong pitching and seems to be on a roll, but Houston has a well balanced team. If I bet on MLB, I'd find it hard not to bet on Houston.