One thing I like about the multiplayer is that all classes are actually viable, tried all 6 and found no trouble using all 6.
Since it was a demo I was trying a few non-standard or non-optimal builds. Favourite was asari adapt with stasis bubble and the widow sniper rifle, hold them in place, take my time and line up a perfect head shot. Also the stasis bubble was amazing for guardians, phathoms and nemesis. Cleared gold with my asari adapt bubble sniper (the term I coined for the class).
Also had alot of fun with a Salarian infiltrator with a shotgun. Dies super quickly if I don't pay attention but just pure fun.
I never unlocked the Krogan solider but it did look fun, tho in my experience people using the Krogan forgot them were only near invincible not full invincible and as such would die at crucial times.