What's a stockbreaker/stockbroker?

When I found out which companies I want to invest in I came to a stop at a stockbroke option thingie after clicking ';trade now';.The page gave me options on which stockborker i'm goin to use.The stockbrokers were';TD Ameritrade,E trade financing,FXCM,Scottrade,and Share Builder.Which one do i take and does it matter what i choose?