I was going to switch to Track1099 this year, but the Social Security Administration send out notices that they shouldn't be used (they didn't specify why).  Track1099 (Zen) has seems to fixed the problem since then, but it makes to hesitant to rely on their reliability and/or security.

TaxBandits is another highly popular service that I am considering to use.

I've used efilemyforms in the past, but I don't like they they don't allow you to delete old records (too much of a security risk).