Bardock is a much more interesting character because even when I was just a kid he had many times King Vegeta's screentime. And even then, all that made Bardock interesting at all was his TV special that gave him focus, in everything else he is either nothing but a name and a face or, worse, has had what the TV special established retconned and ruined.
I honesty would love a movie or something about the Saiyan-Tuffle war, mainly because from the flashbacks we do see within the anime.(Yes I know filler, but still) Just look really nice and from the dialogue, it sounds like the Tuffles weren't completely outclassed until the moon was involved.
So this could really be interesting see technology vs raw power kinda thing and show how King Vegeta became...well the King.
People likely would've gravitated toward Bardock more regardless because of being the original Goku who pushed himself and surpassed limits but with a more badass persona and stuff. Bardock still went down fighting against Frieza at least in the DBS Broly flashback, so could've been worse as far as the retcon.
I guess to be fair, if we had saw more of King Vegeta beyond generic ruthless ruler whose people hate him, my opinion on him would've been higher. A more in depth look at the Saiyan vs Tuffle war could be interesting, though there'd be little point now unless it brought something to the current story setting.
Aside from that he's had countless what-if's in gaming form, a huge role in Xenoverse 2 in which he becomes a Super Saiyan 3, a spin-off, and so much more.
King Vegeta to my knowledge has never had more then a paragraph of lines.
Hell even in Dragon Ball Heroes where everyone can go ****in' SSJ12 or some shit, King Vegeta still doesn't have a Super Saiyan form.
Not that he needs one but literally every important Saiyan, canon or not, has gone Super Saiyan.