The Partners of Detective Logan
Sergent Max Greevey (George Dzunda) is Logan's buddy. His married-with-kids lifestyle complements Logan's carefree, somewhat secular, bachelor existence. In one of my favorite episodes ("Sonata for Solo Organ"), he giggles like an adorable teddy-bear over Logan's outrageous flirting. Despite being amused by Logan, Greevey sees his life as the more stable and productive. He is also more conservative than Logan as indicated in the episode "Prisoner of Love" where he tries to remove himself from the case because of the victim's kinky lifestyle.
Logan and Greevey, though different, rarely argue or disagree. They behave like men who are thoroughly used to, and comfortable with, each other.
Sergent Phil Cerreta (Paul Sorvino) has a much more fatherly attitude towards Logan. Of all Logan's partners, he most often refers to Logan as "Mikey." Like Greevey, Cerreta is a married man with kids, but he comes across as more at ease in his own skin In "Self Defense," he testifies against the prosecution; although he didn't approach the defense, he makes clear to Stone, without apology, that he will say exactly what he thinks on the stand, even if what he says helps the defense.
Logan often argues with Cerreta, but he will bow to his partner's point of view, especially when dealing with the D.A.s.
When Logan becomes part of the Major Case squad (Law & Order: Criminal Intent), he gets two partners in succession. His first, Detective Carolyn Barek (Anabella Sciorra) is an interesting character but ultimately not a good mirror to Logan (Noth).
To elucidate: D'Onofrio's Criminal Intent character, Goren, needs a "passer"--another character to feed him behaviors, attitudes, and lines. This sounds belittling to his partner (Eames played by Kathryn Erbe), but from a writing point of view, it is a valuable skill, and Erbe is very good at it. (She's so good, it is necessary to rewatch episodes several times to realize how quietly and unobtrusively she helps a scene move towards a denouement. Unfortunately, the ability to "assist" is often ignored in Hollywood--though not, thank goodness, in basketball. Kudos John Stockton!)
Noth's character, on the other hand, needs a mirror--a character that highlights parts of Logan's personality by revealing his similarities or differences to his partners. And Barek was too different, too remote, too self-contained to do this effectively.
Detective Megan Wheeler (played by Julianne Nicholson), on the other hand, is a truly inspired piece of writing/casting. She is perfect as Logan's mirror. For one, Nicholson's unique and utterly bone-centered beauty matches Noth's handsomeness. For another, Wheeler's comparative youth highlights Logan's (slightly) mellowed middle-age plus his hands-on attitude. And her tentative loyalty is something that Logan badly needs.
I do find it interesting, and intelligent, that Noth and D'Onofrio are rarely paired together. Not only are both guys SO HUGE they tend to physically dwarf scenes they are in (hey, is anyone else in that room?), they are both chew-the-scenery guys. With Noth, this is simply a matter of innate and rather remarkable charisma. With D'Onofrio, it is how he tackles scripts, so the audience feels exposed to Goren's inner life in every scene. When they are together, there is rarely any balance.
Apart, however, they've got good partners! And Logan has been blessed with fine ones throughout his career.
(I am aware that the above post skips between discussing the characters from an "outside" point of view and discussing them from within the fictional world. This is the sort of thing that annoys Wikipedia editors, but what-the-hey, I'm aware of both things when I watch a show, so I figured I'd combine them here.)