Good and hard question but I made a recent overall Top 10 er 12 list for the IMDB Steele Board, so ....
I'll put it in Season Order for you and add some others in the seasons that could also easily make the list depending on mood or just because. If you don't want to read potential spoilers for Season 4 then skip the lengthy descriptions and just look at the titles.
Season One:Thou Shalt Not Steele: I've discussed it before. It's episode that shows you everything RS is about and what you get. We get character insight into both characters and their relationship, we get insight into both their pasts. We see the adventurous loving side of Laura and how that attracts her to Steele and we see Steele uber competent and sexy as hell. It's also witty as heck with some great risqué lines and we get a shouting talking over scene.
A Good Night's Steele: (part of what may be the three best back to back to back episodes in the series --
Goodnight, Hearts, To Stop A Steele) I just love the humor of this episode and it has some of the best lines of dialogue of any episode. Five minutes to get though a hospital standard, if the union got wind of this. I don't want to sleep with you, I just want to sleep with you, I think we should give serious consideration to framing that woman, hoisted by my own canard, your lilting voice. Laura initiating a kiss for the first time! Steele becoming the man he pretends to be -- what could be more appropriate!
More: Tempered, License, Belted, Hearts, Stop A Steele, Vintage, Circulation
Season Two:Red Holt Steele: The opening surveillance scene is great -- Laura running and Steele observing the long legged field darter compete with cigar and his paint set behind him. Them there's the Xenos story, if you asked and palm kiss. To top it all off we have Steele wet (but he shouldn't have put his sweatshirt on before he answered the door!) and the beautiful romantic noirish tag with Steele walking alone on the street in his trench coat as Laura plays her gift.
Dreams of Steele: Not only are the dream sequences very funny but they also give some insight into the relationship -- as does the entire falling apart of the case -- capped with the talk in the coffin. The actual mystery of the episode is also very good as are their action pieces and it's all seamlessly integrated.
More: Steele Away Part 1 &2, Love Among the Steele, Steele Framed, Woman of Steele
Season Three:Steele At It: Steele’s expert theft of the dagger (love him all in black though it was very careless of him to toss his scarf away so close to the crime scenes) Laura's chase and tackle of Steel on the beach. The FABULOUS argument scene about how some partners or more equal than others. The Goldfinger wetsuit scene.
Steele Your Heart Away: The best of the non-US episodes (which are some of the best quality overall) Steele the man no one knows the identity of becomes the man he doesn't even know himself. And yet he knows enough that he wants Laura and she wants him. The use of locations is perfection. The supporting characters are wonderful. And amidst this romp Steele's thwarted attempt to find his real identity is poignant and rather heartbreaking. And the tag where Laura, says home Mr. Steele says it all. LA is his home, as is Laura and he IS Mr. Steele.
Have I Got a Steele For You: I adore Mulch and this is his best appearance. But most of all this is the relationship thaw episode and it's a great thaw -- marred only by an interruption by Mildred (comes on get an answering service already and turn off your phone!) And there's another great Steele theft, which always makes me happy -- love the swiping of the Porches. Oh and "George, my dolly" One of my favorite line readings of the series.
Steele Trying: Tony Bennett's music (mercilessly removed from the DVDs in the U.S. I wonder if it's there for the U.K. discs that will come out) completely makes the episode the unique experience it is but even without it's a top notch episode and the dance scene would probably put it in the top 10 anyway. Swoon. The mystery is good as are the locations, the fast pace and the humor. "You were the professional in the relationship" Ha! Oh favorite moment with what could be a throwaway action scene -- Steele using the stripper pole to his advantage in the fight scene and then topping it off with kissing the stripper on the top of her head. LOL
More: Lofty, Gourmet, Diced Steele, Puzzled, Now You Steele It, Approval
Season Four:Forged Steele: Steele waking up in his underwear -- and then it just gets better. It's a fun complex mystery though how anyone could think Steele would pull off something so ridiculous and close to home just for $6m and then hide some of the diamonds in his cheese well come on! Still we get Steele and Mildred breaking in together, Laura's worry then belief then doubts and the jailhouse chin tilt talk. Oh and extra points for how Steele snaps his ID bracelet off the hostesses wrist.
Premium Steele: Monroe-- one of my favorites one off characters and someone I'd like to see more of. I find it completely believable he was Steele's friend. (and Richard Lawson is HOT) The mystery is excellent as is Steele's obsession with his new vcr/wide screen tv. And of course there's the Hotel room scene -- when Laura does say the nicest things he's ever said to Steele. It's a beautiful and touching scene and one where we see them actually afraid which is very rare. "We've got picture we've got sound!" -- Frankly my dear I don't give a damn" -- one of the best tags ever.
Sensitive Steele:The best of the spoofing current fads episodes (better than Suburban, much much better than Alive & Kicking and Running and even better than the good Grappling) I love seeing Steele and Laura in all the relationship exercises -- especially Steele's complete discomfort and disdain for all the touch feeling gack. And of course there's the Gazebo, Bataka, Bataka aftermath and beach scenes. Oh and Steele's sweater -- greatest sweater ever.
Beg Borrow or Steele: I love this episode. I love almost every scene in it. From the not having any energy, to the office tackle, to them seeing their obituaries on TV, to spying on their wake, Mildred getting arrested and the ever-decreasing levels of comfort and economic status they devolve into (the best being the porn theater and the exchanges after). The scene in the homeless shelter when Laura decides to stay and share a vermin ridden bed with Steele is I think the most romantic and loving act she ever did. Now that's commitment! And the end tag scene -- of is that your foot on my leg and his eyebrow raise -- perfection.
More: Steele Searching, Steele Blushing, Steele. Inc, Steele in the Spotlight, Dancer, Prancer, Donner and Steele, Santa Claus is Coming to Steele.