I'd go with the 1/2" shanks. They are rigid and no collet That's just another thing that can go wrong. Use it a lot and it gets harder to stay tight. I was using a fairly large 1/4" bit in a 1/2" collet and I'd tightened the heck out of it. I was working a piece and the bit came flying out it hit the floor right between my feet hard enough to gouge the concrete and shatter the blades.

Steve