Top MatchesI am going to go with Steamboat. Vader has a lot of great matches, but you'd probably have to get through 3-5 of steamboat's top matches before you got to a Vader match on my all time list. I have Flair/Steamboat from 4/2/89 in my top 10. I no longer have a Vader match in my top 100. That said, if it were a "favorites" list, I'd have at least two Vader matches (the second Takada and the Sting strap match) pretty high. So eve though its fairly close, Steamboat has Rude and Flair's best matches in my mind.... I can't deny him this category.
Winner: Steamboat
Versatility
This is maybe the toughest one to call. Both men where physically gifted in a way that allowed them to be relatively versatile in the ring. I am going to give a slight slight edge to Vader though because where Steamboat more or less was the same dude most of his career he wasn't able to be that dude in as many different places as Vader, at least not with the same success. Particularly, Vader's ability to produce a few really good shoot style matches (limited as he was in that context) stands out. I think if you look at it on a micro level they are basically a draw here, but Vader getting over in Japan and the US edges this out.
Winner: Vader
Consistency
I am going to have to also go with a draw here. They both developed styles and had skillsets that gave them high floors. Even in what is considered a "down" time for Vader in the WWE he was kinda great a lot of the time.
Winner: Draw
Charisma/"It" Factor
This one feels really close to me. Steamboat was the prototype babyface. He is handsome, athletic, and just projected everything through the screen. On the other hand, Vader is presence. All he has to do is walk through the curtain and he is a legit threat to everybody in the room. I think this boils down to two things that sum up their persona. Steamboat coming out with his family vs Vader having a giant helmet that shot smoke and sparks. The helmet with smoke and sparks gets this by the narrowest of margins.
Winner: Vader
Promos
Man, this comparison is really tough. Their strengths and (relatively) weaknesses are so similar. I am going to Vader because I loved his over the top promos and vignettes in WCW. The white castle of fear one with sting is still one of my favorites. Steamer could be a really good up the gut promo and was probably more consistent, but Vader is more memorable to me.
Winner: Vader
Elevating Others
This is one I gotta go Steamboat on. I totally get the argument for Vader, but I think Steamboat could make just about anyone look good and I'm not sure I can say that for Vader. Don't get me wrong. I think if he wanted to he could. He had the skill to, but just in terms of the era and his position in wrestling at the time... structurally he couldn't go out and make everyone look great. Steamboat not only could, it was sort of his job.
Winner: Steamboat
Offense
Yeah, I agree with Elliot. You can't give this to anyone but Vader. Vader is an all timer in terms of offense. It isn't just what he does. Its how he does it. He puts so many little tweaks and nuances into how he executes moves to make them HIS. When you have a variation of a power bomb named after - given that virtually every remotely big man in wrestling history has done the power bomb - you are good at offense.
Winner: Vader
Selling
Again, I totally agree with Elliott here. Steamboat sold for the cheap seats. He understood the space he worked in. He understood how to make things look good live AND on TV. His selling may be over the top but you know what else is over the top.... pro fucking wrestling.
Winner: Steamboat
Rewatch Value
Ugh.... on one hand I think Steamboat has the higher end matches and I genuinely love going back and watching elite wrestling matches. I don't often go back and watch hour long classics over, but if was only allowed to watch one guy, I'd kinda want to have a few options in that regard. On the other hand, Vader has some time in shoot wrestling and that really bolsters his resume for me. I think I have to call this a draw. Honestly, if Hansen v Bryan was close in this regard, this is an honest to god tossup. Gun to my head... I'd flip a coin.
Winner: Draw
Elliott's Bonus Question (The Brody/Nigel Conundrum or Best Work Associated With a Bad Wrestler)
I only count this as .5 because I think of it as kind of a tie breaker at best. A lot of what I consider here is considered in versatility, consistency, and elevating others. This one is kinda tough, but I think I might have to give it to Vader. He worked with Sid as a team in WCW and as rivals in WWE and while I wouldn't call any of it GREAT I don't recall it being terrible.
Winner: Vader
Count
Vader - 4.5
Steamboat - 3
Draw - 2
Virtually all of these categories are pretty close to me. I could imagine feeling differently about quite a few of them in the not too distant future. I'll give the not do vader for right now though.