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It will also deppend very much on which class I'm playing. I think I would best describe them as first picks, rather than best or worst. Her unlock able Warp Ammo is useful if you are playing biotic and did not choose it as your own bonus power, but that is a pretty narrow circumstance. Jacob/Jack- Jacob can't deal with shields or armor, but if you do the Garrus recruitment mission early he is vital to stop regeneration.
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Grunt- is useful on Collector IFF and Horizon, since he can withstand getting swarmed by husks, and his shotgun is great at close range, but he doesn't have any ability to deal with shields or armor. Mordin can be useful in certain situations on Insanity, but he doesn't get neural shock until late, and by then you have much better options. However, I give her a boost because she absolutely murders the collectors during the suicide mission on Insanity, throwing husks, setting up detonations, dropping armor and barriers, and stunning enemies with Reave.
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Samara- she suffers because she doesn't get Reave until you do her loyalty mission, and she is pretty useless up to that point. Thane- Warp and Throw are a nice combo, and he is useful right after recruitment since shredder ammo is worthless. Zaeed- disruptor Squad Ammo- it's available right from the start, so you can leave his loyalty mission until late in the game. I know it's situational, but there are a ton of missions with Geth or Security Mechs. Tali/Legion- these two are basically interchangeable, since hacking is their most useful power. Garrus is next, but he doesn't really shine until you unlock AP squad Ammo, but once unlocked- WOW. She has warp for Armor and Barriers, Overload for shields, and her passive gives a bonus to everyone else! Just as important: Slam is worthless, so you can use her best talents from the start. Miranda is the most important and versatile squadmate by far. It depends on what difficulty you are playing and who the enemy is, but overall, the ability to quickly drop shields and armor is the key.
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