That is a matter of personal preference!
The better question is, “What groups should I join?” There are three main reasons why people join Groups on LinkedIn: professional association (others in your industry looking for and willing to offer tips and advice), target market (the group attracts the people you are looking to meet), or personal interest (even these usually go back to business in some way).
When you look at groups from this perspective it helps making the decision of which groups to join much easier. Joining groups gives you the opportunity to meet the people (that you do not currently know and) you really want to meet. By participating in conversations you can get to know more about them, how they think, their interests, and what is important to them. So when you do reach out you will be able to structure it in a way that is of interest to them.
Participating in groups is vital—if you want to produce any results. Just belonging to a group is a waste of time, only liking conversations shows minimal involvement and gives no reason as to why anyone should remember you; but commenting on articles and in conversations does!
Remember, people can only read what you write. They can’t hear what you are thinking and most of them will not know you—so read and reread what you write to ensure that it can’t be misinterpreted.