I really like Miquon. It is deep and flexible. Get the Orange and Red books and let him self select which sheets to do...
I also really like MEP. It starts shockingly easy but mixes in challenges very early. The first couple of weeks, you are insulted by it but then you start seeing the puzzle problems and it all makes sense.
Singapore is great but all of the deep problems are in IP and CWP... That's fine but I prefer to have them mixed in...
For DS, Dreambox was completely worthless. He spent more time learning to use the mouse than learning math. Allowing progress based on speed with a computer is ridiculous at this age. The teaching seems great but is very inflexible. The box factory units should be great for teaching place value but if not... there is no other option. MEP, Miquon, and Singapore all present the material in a wider variety of ways and you can adapt them to your kid's strengths. It is more parent intensive but also more effective.
