Allrighty, ranking time.
Undisputed greatest squad member and biggest bro of all time tier:
Garrus - no doubt. There is no Garrus without Shepard and no Shepard without Garrus
Awesome tier:
Liara - I love her for never doubting Shepard and being there when she needed her. An Excellent Bro
Wrex - Shepard
Mordin - a scientist with a conscience and capable of seeing past his own failures. Good qualities. Also, can sing musical songs. 
Legion - A robro. If Garrus didnt exist he would be bro no 1.
Good tier:
Zaeed - A Good Bro. Would rank higher if he had a bigger part, but bonuspoints for his guddamn nostalgic waxing.
Tali - i love her VA, and she had a lot of bad luck in her life. Girl deserves a break.
Kasumi - A Good Bro, but should spy less on people.
Jack - I didnt really care for her in ME2, but ME3 made her a cool character. Needs a better wardrobe.
EDI - loved how she developed in ME3. Her outfits, meh.
Grunt - would be awesome tier, but Wrex is clearly the better krogan. Bonuspoints for being metal as fuck against Reapers though.
'They're okay, I guess...' tier:
Miranda - I liked her for some reason, even though her face went into uncanny valley territory. Deserved a bigger part in ME3.
Samara - mrs bland.  Needs a better wardrobe.
Thane - mr bland.
Ashley - space racist but loves poetry. Guess that cancels out, leaving her in the nothing special category.
Shit tier:
Javik - cant say i really care about him and his superior attitude is annoying after ten mintes.
Why do you even exist tier:
James - lol
Jacob - the priiiiizzzzeee.
Ashes on Virmire or otherwise dead
Kaidan 
Morinth