This useful website (which is unfortunately on the verge of shutting down) keeps track of the voting behaviour of the Members of the European Parliament.
They can be ranked on several issues. One is the loyalty they show to their political group, found here. It shows that around 75% of MEPs vote with their group at least 90% of the time.
Another ranking, to be found here, shows the rate of attendance. 173 MEPs don’t manage to be there 75 percent of the time.