I voted Staraptor, but it's a clear cut tie between Swellow and Staraptor. Swellow was just as inconsistent in-between showcasing though, doing almost nothing as a Taillow till it's evolution episode. From there on out it defied all everything. Even then, this was the same Swellow that could only tie with Marrison's weaken Gligar, despite the fact it was not used in battle beforehand. How that translates to beating Hariyama and taking Rollouts from Donphan (even though unboosted), I'll never know. If I had to suggest why Swellow looked better, it was because only Pikachu, Groyvle, Chorpish, and the bird itself got any real hard time focus in the Hoenn league (Hoenn altogether really). Staraptor one the other hand, never got full time to itself, though it managed in it's time to complete feats of it's own. Contrary to popular belief, Paul's Weavile is not weak (even if it's never shown onscreen)... no way with what was displayed by Paul would he have kept Weavile if he deemed it weak like others like to claim, no he still has it as we saw it at Regi's house after Paul's defeat to Ash in the league. Staraptor taking Torterra's Stone Edge before also tanking a direct Blizzard proved it could be up to the task of Stamina. It then goes an takes blows to the back from a boosted Metal Claw multiple times, then counters the Claws with Close Combat before charging straight through a final Blizzard with Brave Bird, taking the recoil with it. Earlier in the series, it took out Paul's ridiculously powerful Honchkrow, who's only other lose was as a Murkrow to Cynthia's Garchomp.
If not for screentime issues, Staraptor had a legitimate shot of surpassing Swellow, because it showed some impressive feats as a Staravia as well (taking on all 3 of Maylene's Pokemon, surviving attacks from Honchkrow). But there's honestly no way of saying who's better because they have yet to battle each other (and likely never will) or at least a common foe.