Ripley, I mean, Sigourney Weaver. She’d be believable in the Captain’s chair.
"You let Mudd sell you WHAT? An unknown alien organism? Let me see one! Oh, they’re adorable! Now, go collect them all and shove them out of Airlock three!
Now I want to see how Edward James Olmos would operate within the constraints of a Starfleet commission. 
And Evelyn Martin as first officer.
“Fire a warning shot across her bows, Commander Angel.”
BLAM
“Dammit Angel, I said across her bows!”
“Lucky Shot, Jimmy! Besides, they might have shot back.”
Chekov, as I understand it, was navigator, weapons officer and back-up science officer so… yes, kind of a muddled career path.
But he was the exec of the Reliant, which was destroyed in the second film, not of the Grissom, which was destroyed in the third.
I’d’ve been happy with the mirror-universe bearded Spock in command. What the show really needed was some tough-guy ruthlessness, but don’t take it to cartoonish lengths where people are getting assassinated left and right.
More, “I have had it with these motherfuckin tribbles on this motherfuckin shuttlecraft.”
But, Neelix, I wants Captain Neelix.
I would have to review TOS closely to be confident about this, but I took his move to Tactical Officer aboard Enterprise (TMP) and later Reliant (TWOK) as a career advancement for him. TOS-era Enterprise had no tactical position, suggesting that Starfleet had not yet specialized that position. Weapons control seemed to fall to either the navigator or the helmsman* depending upon the whim of the episode writer. By TMP’s refit of Enterprise, there was a separate bridge station and, consequently, a bridge officer position just for Tactical. Since we’d seen plenty of evidence that extremely junior officers could fill the navigator position by then, I assumed that it was a step up.
As to being backup-science officer, that’s clearly a role he fulfilled on every ship he served on. I’m guessing he minored in science officer at the academy. 
- Or, if the plot really demanded it, someone down in auxiliary control.
But…Dear G-d man, his feet!
“Man, you the one that should be on Spock’s Brain detail!”
Chekov was tactical officer in ST:TMP and had some sort of Security responsibilities in the later movies. Oddly, he is the one who responds with the security team to the phaser demonstration in the mess kitchen and dismisses them when it is a false alarm, but has to have a cadet explain the alarms. (It’s plot exposition, it has to go somewhere!)
Captain Jack…
Sparrow or Harkness - either would be fun.
In ST:TNG “The Best of Both Worlds, Pt. 2,” as Riker and Shelby are looking over the debris of the Starfleet task force at Wolf 359, Shelby referred to the wreck of the USS Chekov, but it was later overdubbed to become the USS Tolstoy. Too bad. It would’ve shown that Chekov really went places in his career - probably an admiral, or an esp. noteworthy captain: USS Chekov | Memory Alpha | Fandom
Among the non-Trek actors who I think could’ve done well in the big chair:
Jeff Daniels
Angie Harmon
Denzel Washington
Judi Dench
Mark Harmon
Dana Delaney
Edward Woodward
Ingrid Bergman (she lived until 1982 - it could’ve happened!)
Poor Chekov. There’s an Urban Legend about his role on the TV series: Was Star Trek's Chekov Inspired by Pravda? | Snopes.com
With that muddled background, I guess it’s no wonder he floated about as a senior sidekick.
Scott got to the rank of captain, but I don’t believe he ever commanded a ship. McCoy is an admiral in the TNG premiere (yeah, I know they never say his name, but it’s DeForest Kelley in the demeanor in the role makes his identity obvious), so at some point he was presumably a captain, though I doubt he ever commanded a ship. I tend to think Uhura & Chekov retired as commanders.
I’d say Brian Blessed, but that may not count as he’s perfect for just about any role.
What about Paul Reubens? Out of the PeeWee character he’s a good actor and can pull off the serious setups. In character, well, that would be awesome. “WE ARE THE BORG” … “I know you are but what am I?” … the Borg would eventually implode. Bonus: we all know what the holodecks are used for anyway.
Mr Bean
I heartily agree with the idea of Capt. James Rockford. He’d be the only captain capable of barrel rolling the Enterprise and leaving skid marks in the ship’s wake.
First Officer Martin, on the other hand, would trade the Enterprise to Harcourt Fenton Mudd for two shiny Buffalo head nickels in a get rich quick scheme.
I wish, after all these years, some Russian-speaking Trekker would actually go and look in the Pravda archives of 1966-69 to find the legendary editorial that supposedly led to the creation of the Chekov character.
I agree. Both of these actors would make excellent captains.
See, this is the kind of outside-the-box thinking I was hoping for. I think she would be fantastic!
:smack: Godsdamnit, I should know better than to throw out ship names off the cuff. I knew Chekov was Exec of Reliant. I think I was so fixated on what a lousy skipper Captain J.T. Esteban was that I mixed them up in my head. My apologies to the late Captain Terrell.
You know, all kidding aside, I can see that. He’d have a little bit of the Jim Kirk fake-it-til-you-make-it about him. I could totally see him coming up with the Corbomite Maneuver.
A weekly television show is beneath either of them, but I’d have loved to see either Jodie Foster or Julianne Moore in the Kate Mulgrew role on Voyager.
Of course, I’d also have liked Janeway to not have been written as a bipolar, delusional, occasionally murderous harpy.
Well, yes, that’s the point. You can’t make every episode about time travel or the holo deck.
Rockford: "You gave Mudd what?
Martin: “Just the ah…ahem. warp core.”
Rockford: "For tribbles?!?!
Martin:“Aw, Jimmy, they’re adorable! Girls love them! We’ll be able to clean up at Star Base 12!”
Rockford:“And just how are we going to get there?”
Martin: “Aw, you’ll think of somethin’, Jimmy.”