Hi!

Well, both are really great programs. I don't really see myself ever not modeling in Silo. It's just really fast and easy for me (big part that...for me) to get a model done in the program.   Modo  is very powerful and also allows for speedy modeling if you use a blend of box and edge modeling. I've not tried just box modeling or just edge modeling in it, so I can't say how fast my experience has been. Keep in mind, I've been modeling for about 10 years now, so I've an advantage not everyone will have. 

Silo is a modeler...unless there's an act of god (or the economy) Nevercenter will keep it a modeler.  Modo is fast on its way of being a full featured app - it's only missing bones for character animation and not all of 401's features were announced...bones could be coming.  The two really complement each other but I'd have to say if you're looking for something you can texture and render in as well as make your model and those were your only choices, then Modo is the way to go and I can say that despite the fact I prefer modeling in Silo.