TL;DR – Lifeline, Wattson, and Pathfinder
Well the game mode has been out for not even 3 days and I feel confident that these legends are the most useful for Armed and Dangerous. Of course every legend has their own advantages but this is why I chose these three
Lifeline – since overall loot is more rare you’re going to
have trouble looking for heals, lifeline’s drone is a MUST. Also her passive shield when reviving teammates is helpful in sniper battles when both squads keep picking at each other from a distance.
Wattson – if you’re lucky enough to find a shield you’re gonna have to recharge it, and that’ll be a problem if you can’t find any cells or batteries, this makes her ultimate much more important in this game mode than in a regular match where everyone has enough shield cells.
Pathfinder – he’s helpful here for the same reason he’s helpful in any game mode, he can give you high ground and use his zipline to escape the ring if you get caught behind it. (And if you don’t have any heals you’ll want to stay out of the ring as much as possible)
Source: https://www.reddit.com/r/apexlegends/comments/czqxfy/best_legends_for_armed_and_dangerous/