There is no big difference between the houses. The biggest one is their homemap for the scrims but even that is history from now on..
So if you are in the process of deciding which house to join ask yourself the following questions:
-Do I know anyone from this house?
-Did I see a lot of this house's guys on my favourite eGO servers?
And if you really have no clue which house to join look at the rosters of the diff. houses (you find 'em as stickies in the house's recruuiting forum) and join one of the smaller houses to support it.