What are the best type of computers to use in a network?

Linux

It would depend on what you mean by networking. Macs play nicely with everyone. Linux/Unix somewhat and Windows not really at all. This is if you are looking at just simple network structure as in a home or small office.

If you are looking at hosting bigger and over the internet I would look at going with Mac or Linux. I am a Mac guy fully because of all the pros it has over other OS', but I run my server off a Linux box. I feel that unless you are running a whole network of Macs or need Mac specific applications on a server then most of the time your standard Linux box will do. I mostly run Linux because it is free to download and I got a PC from a friend that I did some work for. Linux is cheap and is really as solid as a Mac in most aspects. Also with Linux you can run some Windows apps that are required for Serving some things like MMORPGs. Mostly you can run a server off of anything you have. You would just need to run the server software on your PC (Linux Windows or whatever) or Mac and you should be set with few problems.