Titanfall

I found the best way is to equip the archer rocket, the spitfire and play a long game mode such as pilot hunter. Make this your goal to just take out Titans using the rocket, so I wouldn't worry about winning. If you have the slammer unlocked for the spitfire, use that as it works really well while rodeoing the Titans. Aim for auto titans as they are fairly easy, and try to stay in buildings on the sides of the map that overlooks the middle, as most Titans just battle out there. Follow around your friendly Titans, as most other enemy Titans will focus on killing the Titan as opposed to you. Good luck!

Edit: Credit to Ehrenfried who pointed out as an alternative to use a cloak to rodeo onto a Titan. Shoot a full magazine of r101 carbine into it. Before jumping off throw a few satchel charges onto the titan and detonate them. This does a ton of damage.

I decided to give this a try on Frontier Defence and can confirm that it works.

The titans are also much weaker, 2 Archer rockets were enough. I didn't even bother with amped. They travel much slower and actually would harm your chances with the weaker AI titans.

Good luck!

Two words: Frontier Defense. I got this achievement without even knowing about it.