I use Singapore as our main math curriculum and Miquon for reinforcement. Sometimes I've found that when ds is having difficulties understanding a concept in Singapore, the way Miquon works through it can help things finally click. Sometimes this means we work concurrently in both - the Singapore lesson first followed by similar pages in Miquon for more practice. Other times, we might work through the unit in Singapore all the way through and use Miquon as review material while continuing ahead in Singapore. Still other times, it might mean that we don't use Miquon at all.
We use the HIG, textbook, workbook, and IP for Singapore plus the workbooks, c-rods, rod track, and Lab Sheet Annotations from Miquon for the appropriate grade level. I have an assortment of manipulatives with Singapore, some of which I already had on hand and some that I bought specifically to use with it.
Next year I'm not entirely sure what I'll do. I'm thinking about adding in Singapore CWP (because ds seems to enjoy word problems) and dropping Miquon altogether. I haven't quite decided for sure, but I did find that combining both Singapore and Miquon the past two years has worked wel for us.
ETA: There is a chart online somewhere that shows where both Singapore and Miquon cover similar topics that was helpful in planning things out at first, but it's not on the computer I'm using. Maybe someone else here might have it.