I really disagree. IMO Miranda and Tali are the two best with Samara a veeeery close third.
Miranda goes from being a Cerberus loyalist to defecting from Cerberus. Her loyalty lies with her family above all else. She's genetically tailored to be perfect yet chose to rebel against the man and life who gave her those gifts in favor of freedom for both herself and her sister. Tha
Jacob is... really flat. The problem with him being so prim and proper is that it came at the expense of his personality. When he confronted his father instead of feeling... anything... towards him I felt more like I was just relieved the quest was over. Jacob's reactions throughout the mission were just underwhelming and at no point does he really seem to develop as a character.
Garrus is a bro. No doubt about it. The only problem is that all his development happened off-screen. That annoyed me to no end especially since I was hoping to get to explore more about what happened in the time between. Even a quick bit following his mission where you could explore the base and interact with some of the objects from his squad would have gone a long way here.
Jack... UGGGG!!! I hate her. She's a rebel who rebels for the sake of rebelling. A directionless loose cannon with emotional baggage. While ME3 did show she finally found something to care about which was REALLY good I can't help but feel like... it was the writers attempting to save an otherwise-unlikable character instead of a natural progression of her character.
Mordin is fun as heck. He's always surprising me. I really like him. Which is why it's a shame that they make the genophage a huge part of his backstory and character. Especially since, as time has gone on, I've come to side against curing it despite the game HEAVILY pushing for curing it to be the 'good' choice. Makes the mission in ME3 so annoying because I would have to betray two characters I like, including one who knowingly laid down his life, if I wanted to avoid curing it.
Thane. Exists. My issue with Thane is really simple. They were trying for the dying assassin with one last job... which could have worked if he actually DIED in 2. Instead it gets waylaid till 3 unless you're a putz and I feel that's a bit too long both in and out of universe for his character to work.
Grunt. Grunt almost works. A tank-born super soldier engineered to be the perfect krogan. It ALMOST works! Except he turns out to just be Wrex Lite. Wrex is cool, yes, but I never felt like Grunt really grew into his own distinct character in either 2 or 3. Instead he was more of just 'we need a Krogan but Wrex is on the planet' than anything else. If he had developed his own hobbies or something I would have a much higher opinion of him. Like, I dunno, have him and Ashley get together to read Hemmingway, or Grunt start to admire Justicars or value the subterfuge of the Shadow Broker or just... Something more distinct from Wrex. Maybe have him try to pick up genetic engineering from Mordin because of his unique birth.
Kasumi: Really liked her. Too bad she's optional DLC at best with only conversation snippets for interaction and a minor cameo in 3.
Zaeed: Pretty much the same problem as Kasumi. Optional DLC character with only snippets of conversation. Made more annoying though by the fact that SO much of his problems would have been resolved or not existed if he had just told the truth from the start and such. Second-worst companion in 2 easy.
Tali: Tali grew as her own from the naive girl in 1 to the mature leader and potential heroine she is in 3. 2 is a solid stepping stone on that road especially since she's given a hard choice effectively between her identity as a quarian and preserving her father's legacy. Especially since it also is a huge part in deciding if the quarians went to war or not. Too bad 3 messed this plot point up BADLY and they went to war at the stupidest possible time.
Samara: Effectively an Asari Paladin. She seemed really flat and her acquisition mission doesn't do her justice. Then comes her loyalty mission in which she has to kill one of her own daughters. A daughter she loved but, at the same time, is condemned to kill because she's effectively an asari vampire. In 3 she even opts to potentially kill herself instead of offing her final daughter. Really love her as a character. Such a shame her intro mission is garbage.
Morinth: If you have her on your team you're an idiot. Especially if you romance her. Terrible character through and through and only exists so people can continue to have an asari on the team if they killed Samara.
Legion: Whooo boy. This is going to annoy people so much. I do not like Legion. Plain and simple. The Geth 'redemption arc' did not go over well for me. First off, they have a rogue faction going about but don't bother to tell anyone that the two factions are different at ALL? Then they act confused as to how the rogue geth could be so different despite them literally having come to worship reapers and other things? Did the Geth shut off every radio and television in Geth space and shoot the space newspaperboy when he came around? Geth issues aside, I REALLY don't get why people like him. He's there for only a short bit in 2 and he's largely absent in 3. Even in 2 he... feels static as a character. Which is really bad when his loyalty mission basically resulted in me having to choose between brainwashing or destroying literally thousands of other Geth. Not only did I hate that decision (brainwashing vs. death) but Legion doesn't really react or give it the gravity it should have. Placing it right at the end of the game was a poor choice as well since it meant I had to interrupt saving my crew to do Legions mission. That felt SO wrong to me on every level. It would have made a lot more sense if he not only joined earlier but if he had reacted with more gravity regarding the decision there.
And there we go. I know at least some of you will say it's terrible but that's how I felt about the ME2 companions.
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I am the gentle hand who heals, the happy smile who shields, and the foot that will kick your ***! - White Mage