Getting a hang for the Engineer, Adept and Sentinel classes.
Adept is pretty badass (especially the human one), with Singularity + Warp for Biotic Explosion. You can take a shitload of Armour from Banshees and Brutes if you manage to get a few Cannibals in between them for explosions. For weapons, I use my old trusty Carnifex pistol...that thing packs a mean punch and it's pretty easy getting Headshots with it
Quarian engineer is a tricky class to play at first, but with the right weaponry it can be pretty deadly. I tried using both the Disciple and the Geth Plasma Shotgun with her, but it just felt off. I fell back to my trusty Carnifex and it's been one heck of a ride with Sentry Turret (W/ Flamethrower) and Incinerate.
As for the Sentinel, only tried the human one, with Tech Armour, Warp and Throw. If you have a M-37 Falcon Assault Rifle, this class is damn fun to play as. Toss a couple of Falcon rounds, Throw enemies around, rinse and repeat for a shitload of kills. It's pretty fun when paired with an Adept class for crowd control (seriously, Biotic Explosions and the Falcon clears mobs like no tommorrow).
Still....I love my infiltrator class too much to give it up 
By the way, my N7 is already at 142, but I haven't promoted anyone since my first (and only) Infiltrator promotion, i'm only trying to level up each class to 20 to see which i'll promote. Also, I have a question for the MP users: What kind of packs do you buy? Do you usually save for Spectre only or do you buy more Veteran packs?
Current PC Build
CPU - i7 8700K 3.7 GHz (4.7 GHz turbo) 6 cores OC'd to 5.2 GHz with Watercooling (Hydro Series H110i) | MB - Gigabyte Z370 HD3P ATX | Gigabyte GTX 1080ti Gaming OC BLACK 11G (1657 MHz Boost Core / 11010 MHz Memory) | RAM - Corsair DIMM 32GB DDR4, 2400 MHz | PSU - Corsair CX650M (80+ Bronze) 650W | Audio - Asus Essence STX II 7.1 | Monitor - Samsung U28E590D 4K UHD, Freesync, 1 ms, 60 Hz, 28"
