What are the four factors that decide what committee a congressman will join

The first factor is is that if you're capable of conducting governmental investigation then you would join the Standing Committee. It is a type of a permanent committee that exists for the purpose of dealing with any of  the problems that need constant consideration. There are 16 such committees in  the United States

The second factor is based on your capabilities to study a particular governmental issue which is when you join the Select Committee. A select committee is formed when a new problem arises and these committees solve these problems and then stop existing. Their purpose is to examine a certain issue and investigate it.

The third is for those that have a connection between houses and can conduct business with them which is when they would join a Joint committee. Joint committees are formed from members of both houses of the congress and they commonly have very narrow jurisdiction and do not report legislation to the congress.

The fourth is for those who have connection between the house and the senate who then join a Conference Committee. Conference committees deal with solving issues regarding legislation. If the two houses of congress can't agree on legislation, a conference committee is formed to help them resolve the issue.