Should you choose your committee members or should your advisor?

You first have to check to see what the university rules are for a Ph.D committee. Many universities have rules that limit the number of external members, the number of members not from the department, the number of members that are not "regular faculty" and so on.

Assuming that you've checked all those constraints, then you should definitely discuss this with your advisor, who will have more experience in constructing committees in your area.

Which brings up another issue: community norms. In your field of research, are there customary roles that committee members play ? that's something you need to discuss with your advisor.

Finally, after all of the above, to answer some of your questions:

Should you already know them?

Not necessarily, although that helps with the first approach. It helps if they're familiar with your work even if you don't know them personally.

Should they be doing research related to your dissertation topic?

Not necessarily, but they should have some connection to your work, otherwise they won't be able to provide any kind of useful feedback for you.

Should they be in your discipline?

Definitely, unless your topic is interdisciplinary and you want the input from someone in the other discipline.

Should they be selected more for how much they'll help you get a job?

That's definitely a factor. It's not a critical factor for all members of your committee, but it can be a factor when looking for an external member. Ideally, if you're able to do some research with members of the committee, they can write a letter for you.

Bottom line:

• talk to your advisor and discuss all of this with him/her
• Different members of the committee can play different roles. The mix is what's important

There are many ways to build PhD committee, which depend on the local system (country, etc.) and your field. But, here are some general principles that should apply broadly. You need to bring a mix of highly competent yet diverse evaluators, with not too much proximity to yourself or your advisor lest it be thought that you are cherry-picking a partial (friendly) jury for your work.

Regarding your questions:

• Is it more important that your advisor already know your committee members or that you do

  I don't think it's a very important part of the decision-making. Certainly, you don't want the advisor's best friend (or yours!), that could make people think you're scared of unbiased questioning.

• Is it better to get someone in your discipline or someone doing more related work

  Here's one of the factors that play a very important part, for me, in picking committee members. First, all members need to be able to have a good understanding of your work. However, it is good that not all of them are precisely expert in particular field of expertise. It helps to have people from other (related) fields, because they will bring a different perspective, and give you the opportunity to highlight not only the very technical details of your work but also its significance for other fields.

• is the dissertation process supposed to be a chance for you to win people over to your side?

  No. It's good to bring people who don't necessarily agree with you on everything, but you should also avoid as committee members anyone overly critical of your approach of things, unless you know them well and they can keep it under control and agree to disagree. Otherwise, you risk that person actually coming to your defense to win you over. I have seen defenses being “derailed” (though all ended well) by a committee member who was overly argumentative, and it wasn't a nice experience for anybody involved.