Pokemon viability differs from meta-game to meta-game, and whether you're playing in game or online/competitive. That said, I'll briefly review the ones you've mentioned in a general sense:
Pidgeot:
While the base form is sub-par with good speed but poor offensive stats, the mega form actually puts in some decent work, with No Guard STAB Hurricane (and Heat Wave for coverage) and a Special Attack Stat of 135. It is fairly quick at 121 Base Speed, but far from the best Mega evolution out there, so you'd be wasting a Mega Slot. Overall, would not recommend.
Noctowl:
Noctowl is surprisingly bulky, boasting of a 100 HP and 96 Special Defense. It also has access to a number of Psychic type moves, but its Special Attack (at 86) holds it back from shining as an offense oriented Pokemon. However, it has a number of good support moves and the bulk to pull them off, supporting the rest of your team, so you could try it if you want.
Swellow
It's a shame Swellow's offenses cap out at 85 and 75, because it has a great 125 Base Speed. It has some potential both as a Physical set with Guts, as well as an unlikely set in Specs Scrappy Boomburst. If you have access to a Flame Orb, you should really check out this glass cannon.
Pelipper:
A fantastic support Pokemon which was single-handedly saved from obscurity by giving it one of the most useful Abilities in game: Drizzle. With a solid movepool including Surf, Scald, 100% accurate Hurricane, and support moves like Tailwind and U-turn (as a slow pivot), this Pokemon is a must-consider for your team. While on the slower side, it more than makes up for this in its bulk and Special Attack.
Staraptor:
Here's a Kamikaze Pokemon if there was one. A Reckless Brave Bird from a base 120 Attack hits like a runaway truck, decimating opposition if they're not careful. However, it is extremely frail and vulnerable to revenge-killing or other Pokemon faster than this 100 Speed monster. It gets an extremely hard-hitting moveset with Double Edge, Brave Bird, and Close Combat, all of which force it to hit first, hit hard, and die. Still a solid choice.
Unfezant
Despite an attack of 115 and a Speed of 93, it is underwhelming, relying on Sky Attack to damage anything substantially, which needs a Power Herb to activate, and that too for one time use. It's like a poor man's Z move. Would not recommend.
Talonflame
Ah, the OG of the Bird Spam duo/core, and an overwhelming threat in Gen 6 skies. Alas it got its wings clipped when Gale Wings got nerfed and this Pokemon is back to lower tiers, no longer dominating the OU skies. It still has a brilliant speed of 126, but the poor attack stat really holds it back post nerf. That said, it still has some utility, but that 4x damage taken from Stealth Rock spells doom for it in most cases.
Toucannon
Two words: Beak Blast. This slightly gimmicky move fired off a base 120 Attack is the only thing setting apart this otherwise slow (60 Speed) bird. Honestly not the best of the lot.
Corviknight
Bulk Up + Body Press, Brave Bird and Iron Head, all paired with a respectable 87 Attack (but a slow 67 Speed) and a fantastic typing, this Pokemon previously written off as a worse Skarmory clone has seen decent success in the current meta, possibly shining due to the very limited Dex at the moment. While not the best of what Sw/Sh has to offer, this Metal Raven still packs a punch, and is definitely worth a try.
Edit: As Staka mentioned, Power Trip Corviknight with Bulk Up is another option to consider.
Final Verdict:
Staraptor, Pelipper, Corviknight are all good options to consider. If you have a spare Mega Slot, M-Pidgeot has some good potential as well. However, if you have other Pokemon on your team that would love Rain, then Pelipper is the go-to bird for you. In terms of sheer damage, Reckless Staraptor (maybe with a Choice Band/Scarf, even) can really punch holes in the opponent's side before they realise what is happening.
As for the others, you can flip them the bird with an easy conscience; they're terrible.
Also, I've missed some birds here as they weren't mentioned in the question, but Braviary/Mandibuzz are quite decent in offensive and defensive capacities respectively as well.
