Since you will be getting less interest (from ING) than you will be paying with your mortgage, you should probably look for a different investment vehicle than ING.
If those are my only two choices, then I would keep some money in ING and put some into the mortgage. Remember that money put in a house will reduce total interest paid, but is very hard to get to (almost impossible) if you run into hard times. Your mortgage is against your job not your house (try to refi without a job and you'll see).