I keep my cash emergency fund in ING. One thing I would NOT do is use your Roth as an EF. Even if it's technically possible, you're robbing your future to use it. Personally, i'd take a higher rate path before using my roth because once you pull the funds out of a roth, you can never put them back in.
Once you don't put them in during a year, you also can never put those funds in. Using a Roth for the e-fund simply means you're putting your e-fund money into a tax free account instead of a taxable account. You're not robbing your future of anything.
I am going to go with paying down the mortgage.
Cool. It's a reasonable choice in my opinion. Good luck to you!