I'd agree with
DevilEyes about Brooks' diction - I'm not sure what's going on there, but whenever he speechified he just seemed off to me.
I don't know, I think he's pretty good at being a flamboyant gay guy as well.
Quite. One almost half-wishes there was a TNG episode where some random space whatzits gave Stewart a transparent excuse to show his incredible range as an actor.
[I mean, think about Avery Brooks playing both Sisko and MU Sisko. Or even playing Hawk. No WAY Patrick Stewart could ever pull off 'bad-ass'. He would look completely and utterly ridiculous.
"This far and no further!"
First Contact was pretty much a demostration of how well Stewart could be a badass. Whether that's a success is debateable, but I'd call it several mites above "utterly ridiculous."
Or think about a character (any character) losing control of their emotions...from breaking down in tears to outright going postal. These are not parts for which Patrick Stewart is well suited.
He's done both as Picard, and I think he handled it fairly well. The writing in
Generations may have faltered but he did sell that moment. "Sarek" is, as observed, another stellar example.
And just for the record, I do not think the best lead actor in a scifi show is Avery Brooks (in case someone wants to yell 'bias!'). IMO, the best lead actor in a scifi show would probably be Richard Dean Anderson. Or maybe David Duchovney (who convinced me SO MUCH that he 'was' Fox Mulder that I have had a REALLY hard time accepting his character on Californication, partially because he has now convinced me that he 'is' that guy - who is in about every way possible the exact opposite of Fox Mulder!

) or Edward James Olmos.
And in Trek, I think I might give that crown to Kate Mulgrew, actually....
Eh. I haven't seen enough of Stargate to have an opinion on Anderson one way or the other (generally I think he's pretty good at being genial and the down-to-earth guy full of pop culture references, sorta like Ben Browder's character on
Farscape, which I presume is why Browder was roped in to replace him), while Olmos I've seen having recently marathoned BSG. He's good, though he does oversell the odd moment by doing his patented stern, stubborn gruffness too much ("Daybreak", the suicide mission). Definitely the only example we've got of the stubborn old guy space opera lead in a post-Picard world, but the crown in my eyes would still go to Stewart. Nobody and I mean nobody speechifies like that guy.
Anyway, while it's a good role and well played, it's not exactly versatile. Look serious, let your wonderfully weary face do the talking for you, growl out a few lines dead seriously and your paycheck is in the mail, Mr. Olmos. He does add quite a bit of subtelty and nuance to it, but even still...
Duchovny is just some guy, I dunno. This X Files thing, never got into it for some reason. As for Mulgrew - eh. Everything I've seen her in, which is very little (um... this arc in
Cheers, does that count?), she wasn't that different from how she handled Janeway.
As for whether I could think of an actor I'd readily consider better or more versatile than Patrick Stewart as a space opera lead... well, nothing immediately comes to mind, but maybe I'll see it in a dream.