mass-effect-3-multiplayer
As of now my Level 8 Salarian Engineer who was promoted not only two hours ago, resetting his rank, is equipped with the M-4 Shuriken V, along with the SMG Magazine Upgrade I and the SMG High Caliber Barrel I
Energy Drain and Incinerate each have the first three levels upgraded, along with one in the Salarian Operative skill; leaving me with eighteen points left.
What would be the best thing to focus on next?
Adrenaline Rush gives you the stats boost despite it not slowing time, probably because that would be difficult to do in multiplayer:
[I]t doesn't slow down time in MP; it just gives you a boost in damage+protection and weapon stability.
This answer to another question seems to indicate that cloaking works. Can you be more specific about your problem?
Edit: I agree with yx. that you're probably just expecting the wrong thing here; as he says, Cloak just makes you harder to target, not impossible to target.
The only thing you can spend your credits on currently is packs. But as the current special equipment pack shows, Bioware might occasionally add some different packs from the standard ones, and those packs might allow you to get certain equipment faster as they might be less random.
As you can see in the description, this special is time-limited.
So in general there is no use to hoarding credits, you'll only spend them on packs anyway at some point. The exception is if you're speculating on Bioware to add some interesting packs in the future, and want to buy lots of those when they appear. But unless you have some inside information, that would be pure speculation and they might never add more useful things to buy.
If you have the most important equipment for the classes you're playing, it might make sense to always keep a certain amount of credits on hand, so that you can quickly act if Bioware puts out an interesting, time-limited pack.
Best Answer
If you want to use him on Gold or Platinum then you should have full Decoy. I'd go so far as to say use either Energy Drain or Incinerate (I'm partial to Energy Drain myself) but not both. Decoy is useful in that it pulls aggro, giving some measure of crowd control. You'll be a bit squishy so get your health and shields as high as possible.