For a 6yo, I would recommend RightStart Math, with one caveat... we haven't actually used it yet lol...
But I've researched it quite a bit and it's probably what we'll use when DD is older, IF she decides she wants to "do math" at that age.
We just did math workbooks from the bookstore when DS was young, tried Saxon for grade 3 with some success but not completely, took lots of time off math, now we're having great success with Teaching Textbooks - also good for the visual learner, I think, since everything is done on a 'white board' 'live' on your computer screen along with the lecture. It's for older kids, though, the lowest level they have so far is grade 5.
I'm impressed enough with the RightStart Math, though, that I'm thinking of doing their middle-school level geometry with DS once he's finished his current pre-algebra, or concurrently, or something.