Personally, I feel there are a lot more inspired choices for an F-Zero character than Blood Falcon or Black Shadow. As much as I like the pair, there's tons of options besides! For example:
Samurai Goroh has been a quite popular pick at points in time, and him using his dual katanas as well as a heavyweight rushdown archetype could work pretty well in his favour to make him different to other picks.
Pico could be an interesting zoner-grappler, being able to land hits from a distance with his various weapons (such as his rifle seen in F-Zero GX's bonus videos,) but also being able to get up close and handle people one-on-one. Of these, I would actually prefer to see Pico - as he fulfils an effective villain role and brings an interesting playstyle to the table.
I imagine Mighty Gazelle could rival Captain Falcon in speed, but would be much lighter and genuinely be in trouble if comboed. However, to make up for this, Gazelle would have a ton of methods to land comboes himself, playing a little like a Sheik archetype of being incredibly fast but relying in comboes to actually K.O opponents. Sure, he's not as popular as the other two, but he could be interesting.
The truey chaotic pick, Digi-Boy from AX could be a really fun pick. With his entire moveset being based around the fact that he's a boy genius, I think the idea of a trapper-zoner playstyle would work well for him, especially if it rewarded close analysis of the opponents at hand.
I don't want to like, put down people that genuinely do want Blood Falcon or Black Shadow, as they are pretty cool choices! These are just ideas I'd prefer personally.