You can use the same State Download twice. If you paid taxes in 2 states, then it wouldn't be enough.
Have you plugged the situation TaxSlayer failed to catch into TurboTax? To see if it catches it?
If your investments are significant, then Premier might make sense. On their website TurboTax says "Investments and rental property" should use Premier. Do you have form 1099-B showing the proceeds from selling mutual funds?
Before you provide your login and password to tax software, I recommend you temporary change it to something the tax software will use. Then let the tax software download your financial information... then change it back. That way the tax software only has a valid password for a limited amount of time. Then if somehow the tax software leaks your password later, it won't impact you since it's a password you're no longer using.