The tanks generate CE faster, but you need one player from each party to gather them, and people to be very coordinated in how they get ce. Otherwise you get people tripping over each other to pick them up. The tanks also stop generating CE when people come in and attack you, because you can't gather them. Mid is slower, but requires less people and is constant passive generation.

The wins I have seen tend to be more about how good your mech players are and how coordinated the team works. CE isn't as much of an issue as you think if you can keep them alive long enough and act well enough to do damage.