According to a Pew Forum survey, Anglicans/Episcopalians are the most overrepresented denomination in the 112th Congress: They hold 7.7% of the seats yet are 1.5% of the adult population. No other Christian denomination is close in terms of over representation although Presbyterians are also heavily over represented.
Anglicans/Episcopalians have 41 of the 535 seats. Although Baptists have more than 50% percent more seats than Anglicans/Episcopalians, Baptists are 17.2% of the adult population.
16.1% of American adults say they are unaffiliated. No members of the House or Senate are unaffiliated.
Read it here.
Addendum. What about party affiliation? Among Anglicans/Episcopalians it's tilted heavily Republican. See this table. While there take a look at Baptists by party.
Thanks to a commenter at our Facebook site for the pointer to this table.