Drop shield is great in Campaign. Its like having your own health pack where ever you go. As for MM, I usually stick with sprint, which surprised me. I thought I'd be using jet pack or armour lock more.
Personally I like the jetpack because it allows you to get to many otherwise unreachable positions even in online multiplayer. The only downside is that you quickly become a prime target.
Me and my buddies find that armour lock is the best to use if you all agree to use it and support each other. You can use it to quickly block two seperate grenades, or just hold it down when your shields are gone so your team can save you.
Didnt expect this to get so many comments haha. And even though the hologram doesnt actually block bullets if you send your hologram while you are really close to someone they will ALWAYS beat it down, its just common halo reactions, while they are helplessly punching a hologram you can punch them and run back and one-shot them. Thats one of my most satisfying techniques with the hologram
Something that I've found really helpful is to go around in groups of two with one person using armor lock, while the other uses hologram. Have the first player send out their hologram, then have the armor lock player go out and attack the opponents. Once he gets the opponents health down, have the hologram player come out and kill the opponents while their shields are down. Very good tactic.
Evade is so awesome, since I can effectively use it offensively and defensively. I love being close to someone and when they are about to melee, I evade behind them and assassinate.
Hologram has to be the most useful one. There are so many tricks and thing you can play around with. A good trick is to look down and leave a hologram just lying there and walk out in a straight line towards enemies. They'll assume you are the holo and then you just turn around and assassinate them. It works as a distraction for enemies by having something walking out randomly. That can confuse a lot of people.
I just about always go with Sprint (or evade if applicable). I'm not so great with Armor Lock because I forget to use it in heated situations, and Camo is pretty much useless now. Hologram is fun, but only works a small percentage of the time. So Drop Shield would be the closest second 'cause I'm a team healer.
jet pack/sprint most of the time. in tough area of campaign, firefight, or an objective multiplayer, its all about the drop shield. I played firefight with 3 complete strangers for a couple hours and to make it easier for them to find me I changed my tag to "DOC" its fun to play medic