For three years I have paid my bills online using the online bill payment feature at Regions bank. I hold both a savings and checking account with Regions bank. I am pleased with the customer service, interest rates, and features each of these accounts offers, so putting my money in an account from which I can pay bills works well for me.
The system is very easy to set up, and from what I can tell it is very secure. Companies with whom you have accounts are entered individually with addresses and billing account numbers. Once these have been entered into the system, they become available through a drop-down menu on the Payment tab. I can literally pay five or six bills within a minute's time AND save myself postage costs associated with mailing in payments.
You can set up payments that are single-time payments, or set them up to recur at regular intervals (like a house or car payment). If you have a Regions Bank credit card, you can simply transfer money from your checking or savings account onto your credit card without having to set up a separate drop-down category.
It generally takes a few days to process bills using Regions online bill paying system, but I believe this is standard. There have been occasions when payment has gone through more quickly, but it has never taken more than a few days.
Overall, I would highly recommend using an online bill payment system, particularly the one offered by Regions Bank.