We use Singapore and our DS really likes it. We like the variety of problems used in their workbook, extra practice, intensive practice, and word problem books.
Our only complaint is the lack of "true" math vocabulary used. This really won't be an issue unless you are a total math geek. :tongue_smilie: For those of us who are geeks, and you know who you are, just use the vocabulary in lessons and math questions around the house. DH and I do this all the time.