Don't purchase anything. Either get Apache (FOSS - free, open source), Tomcat (ditto), or Nginx (also FOSS). Also, run your server on Linux - it is much more secure for this sort of purpose than Windows of any sort.
For a personal website, I'd recommend you host it with a provider. There are free ones out there as well, unless you are doing this because you want to learn about web services/networking, etc...
What do you mean by "best web server". For a personal website at home, you basically need an internet connection, a router that can handle port forwarding into your network, and a computer that is running an operating system, and a web service application. For a personal site, just about any modern computer can do the job at least adequately.
If you are just planning on your single web site another option is to get a virtual system through one of the hosting providers. You could purchase a basic virtual system from one of the hosting providers and get started for a very low cost. They will handle the costs of the hardware, electricity, and maintain internet connections 24/7 for a set monthly cost. You will also have support available for setting your site and installing the software on your server.
Some of the considerations for you to run your own server at the office or at home are:
Your ISP is going to charge you a lot more for a true network connection with a fixed IP address and you will be lucky to get a 100MB connection. Most providers give a lower upload rate than a down load rate and you will need a high upload rate for people to be able to view your web site.
The hardware cost is going to be higher for your initial purchase of a server and you have no idea how well your site is going to do.
You will want a system with redundancy so that if any of the parts fail you don't loose your site.
If your site does well and you need a bigger server and faster connection you are going to increase you cost.
You will also have to consider the additional power needed to run the system and keep it cool all year long.