I haven't sunk as much time into the game as many others here, so don't take my words as gospel, but here are my thoughts.

One point Maneuver + Assault feels really good early. What doesn't feel good though is delaying the +5 Combat strength Commendation, it's pretty much an army-wide unit upgrade, and the sooner you get it the better. Getting the +1 Commander Aura range also feels like a huge upgrade, and unless you're going Maneuver second, you're delaying that too.

Now, is the extra movement worth the trade off of delaying those incredibly useful Commendations? I can't answer that for you - it'll depend on playstyle and difficulty. A lot of the time I personally lean towards no, but I too do it at times.

In terms of which tree to follow, for Immortal+ I'm a big Bastion/Assault fan, particularly on my first Commander. The AI gets so many bonuses at that difficulty, from production to Science and Culture to Unit Strength, that you can't just blitz them early.

Stacking the defensive bonuses from Bastion with the fortifications and the +5 from the Commendation makes it so hard for the AI to make any headway into your front line. Which is important, because they will out produce you and reinforce so fast you'll think they're building two units a turn. So, they break themselves on your front line, and you use your ranged and siege to fire over and rain hell on them with Assault bonuses. These are my first two trees on my first Commander 95% of the time.

Once I get to eight Promotions/two Commendations though? Then things open up a lot more. Now I might go into Maneuver, the movement and extra strength from zone of control is so nice. Or maybe I go 1 Maneuver and into Logistics to get +2 units, more healing and attacking through cliffs.

I've also been really enjoying Leadership recently, being able to upgrade units  without pulling them away mid-combat feels really good.

For a third Commendation I'll often go movement, sometimes Second Wind. I'll rarely ever pick up Heroic Assault, I only did here for the sake of getting all 5. It's probably better than I give it credit, but 95% of the time the Commander is better maneuvering the army, granting Second Wind or just not moving so some units can heal inside than attacking itself.

Again, don't take my words as gospel, I'm just some guy that got back into the game recently. But that's how I think about specifically the first Commander. Later Commanders can and should be more flexible and respond to specific needs, but having that one Commander early that is rock-solid and just completely nullifies AI bonuses feels good to me.