This^ That LMG with the Hammer destroys them before they even have time to react really... even if they deploy electric smoke.
Whilst the LMG with the hammer perk/attachment has been granted from the start as advice for this challenge I'd say that's quite exaggerated to say it destroys them before they have time to react, especially saying even if they deploy electric smoke. It's not that "instant" or rather fast. Unless they've updated the damage dramatically since I did this challenge (which I haven't seen listed & doubt anyway), but any "good" pilot will hear the clanging as you attempt to rodeo the titan and react accordingly. The amount of players using electric smoke is ridiculous. Either way use a weapon you're comfortable with, lots of people say LMG as a go to gun but it's personal choice, I personally stayed away from the LMG after it failed to live up to expectation + it's use on the battlefield.
I've done it as well. If you're shooting when you rip off the protective piece, it doesn't matter if they deploy electric smoke.