I was going to post a threat advocating for a Titanfall line, but it looks like you guys beat me to the punch!
I love Titanfall. I started playing the first game shortly before its sequel came out (which I also subsequently purchased and have been playing non-stop), and I think the license is a perfect fit for Mega Construx. The addition of new Titan and Pilot classes in Titanfall 2 provides for even more possibility for varying sets.
I still think the Halo and Call of Duty lines have a lot of momentum and longevity, and goodness knows they've only scratched the surface with Destiny. However, with the Assassin's Creed almost certainly a thing of the past, there's been left a slot for a new license for the Collector's Series. I vote for Titanfall.