10
Personally I like the Sentinel in 2/3 the best but in 1 they don't really have the specific niche purpose that they seem to in the sequels, since all dual classes just get half of the powers from each.
ME1 I just go full Engineer and select AR training.
It's always AR training.
One of the things I really enjoy about Andromeda is that I can have my toolbox AND flash, by having a Sentinel with Flamethrower, Energy Drain, and Charge! It's been a fun run.
An individual of culture!
I run Sentinel: Biotic Charge, Flamethrower, Cryo beam in Andromeda. I alternate freezing and charging with flaming and charging. When I get bored I swap cryo for overload so I can detonate tech as well as with charge. It's just too damn fun, and being able to choose what biotic power you spec into really makes it fun.
Personally I'd prefer the next game to have classes but allow for freedom of choice in the trees your class has available. Restrict "primary" powers like Charge or Cloak to one per class and make the class evolution look more like "you get two primary power options or an additional two secondary slots" or something. Add ammo powers back in but give them their own slot type, restrict to one for combat adjacent classes and two for soldier. Maybe if you choose to give up the extra primary power slot you get to choose two and can have a combo of ammo and secondary powers in whatever amount you want, etc. Definitely keep passives how they are, I shouldn't have to give up a power slot because I have tech armor, that's just the perk of the sentinel. I liked Andromeda's take on passives and think it should be carried over.
All of these changes would allow for replayability and reduce the Ryder Mary Sue kind of vibe while allowing for true choice within the confines of the class you chose.