Sirius a Slytherin? Convince me!

[jwcpgh]

No: HPFGUIDX 75352

I've seen a number of posts suggesting that each of the Marauders 
belonged to a different house.  There seems to be general agreement 
that James was a Gryffindor (this is canon)and Remus would have been 
a Ravenclaw.  I can see Peter being a Hufflepuff, but Sirius a 
Slytherin? He never displayed the kind of ruthless ambition that 
characterizes that house.   If he had been at all ambitious, he would 
not have broken with his family, who were purebloods and seemed to 
have quite a lot of status in the WW.  In fact, you might argue that 
his unswerving loyalty to his friends would put him in Hufflepuff, 
leaving Peter in Slytherin, where he belongs.  He just doesn't seem 
like a Hufflepuff, though-he's too bright, too brash and too 
reckless.  So what do you all think?  

A possible problem with the theory overall is that I'm not sure that 
making Remus a prefect in Ravenclaw would have much effect on the 
behavior of James and Sirius if they were in different houses.  I 
know prefects can take points from any house, but I can't really see 
Remus doing that to Moony or Padfoot.  Being a Gryffindor prefect 
would at least let him keep an eye on them a lot of the time.

Laura