The main issues for an ISP are cost, support staff, reliability and adherence to standards.  If you run any type of server, you also need a static IP address(s).  Note that an ISP may offer website hosting or domain registering.  To date, I have never seen an ISP offer very good service for this.  An ISP is local while a registrar or website hosting firm can be anywhere.

For now, this website is hosted by Omnis Network and I really like them.  A lot of ISP's require you to install some sort of software to connect.  I refuse to use them.  I have run Earthlink, SW Bell DSL, and Cox Cable modem's (consumer and business services) without any additional software.  I believe that these all have "dialer software".  Windows has all you need to connect to the Internet (and has for years).