Obtain a modem dial-in number for the ISP you're considering and call at the time you plan to use the service to make sure you can get through without encountering busy or no answer signals. Look for ISPs that include commercial licensed software on disk or CD, accompanied by software and Internet access guides. It should be pre-configured with their IP address and particular settings. This can often cause confusion. Having licensed software ensures that you have access to user support and is the legal choice.
Downloadable software is also fraught with inconvenience.
If you're on your own you may feel more comfortable paying the extra money for something more user-friendly. This will determine which package is the best for you. The low end ISP's also tend to offer you the low end user support and capacity. It is often worth investing a little bit more and getting an ISP which is going to serve your needs. Your best choice is not necessarily the least expensive.