In light of the recent change to Akali, would Katarina or Akali bring more usefulness to the table, assuming I had the right team composition to back me up?

Also, is Corki viable as an ADC? I don't see him get much use anymore (bearing in mind I don't play ranked). Just wondering if its worth it to pick him up while he's still on sale or if I should get a different ADC. I already have Ashe/Graves/MF. Been considering Draven...

Thanks for any input on one or both of my questions!

Akali is more single-target burst, Kat isn't really that strong anymore unless you build tank kat and just sit in teamfights spamming w and eating cc. Neither really brings anything to the team per se.

I would say Corki is still viable, but he's probably not as strong as most other adc, so I would advise against just picking him up if you're unfamiliar with him. Draven is without doubt the strongest adc in terms of raw damage from early on, but you have to be really good at microing to catch those axes.
I think you should be fine with MF/Graves/Ashe, since they are all very strong, but fill slightly different roles, so you can adjust to your team comp.

Akali bursts single targets down faster while Katarina has that ultimate that a lot of people hate. I'd argue that Akali just helps the team a lot more since you can burst down that 1-2 enemies that's causing a lot of trouble. Akali is really jumping in, KO 1-2, jump out.
In response to that guy above, I'd argue that building tanky Katarina (top lane) is really just useless. Doesn't do damage and is a waste of a pick to go tank Kat.

I didn't say that tank Kat is the way to go. I detest tank Kat and agree that she is a waste of a pick. But the problem is Riot keeps nerfing her damage because of tank Kats sitting in teamfights getting resets and doing very good damage while being tanky.
For me personally, there's really no incentive to play her at all right now since all she brings is damage, and unless you're perfect in initiations only going in when you know you can guarantee a kill and reset, you will be useless. And even if you're fed, your damage is subpar and you will feel useless.

So yes, right now Akali definitely brings more to the table so to speak, at least she can do her job right, and without being insanely fed to do mediocre damage.