Noivern:
Pros:
Decent all round stats, excelling in Speed
Amazing movepool
Cons:
While its stats are all good, they are average when compared to other Pokemon
Evolves at LV 48, which is super late(rhymes lol)
While it has a good movepool, it is a bit reliant on TRs and TMs(luckily TRs and TMs are easy to get so not really a big con just wanted to point it out)
Until it evolves, it is way too weak to be used in battles
Decent Special Attack, but low enough to miss out on some KOs allowing it to be killed by SE hits
Scrafty:
Pros:
Great stats except in Special Attack and Speed
Great movepool
Cons:
Very low Speed
Reliant on TMs and TRs(like I said before I just wanted to point that out)
Evolves at LV 39, which is kind of late
While its Attack is decent, it is low enough that it might miss clutch KOs
Horrible Speed means its able to be killed easily by faster SE attacks
Until it evolves, it is average
Overall, I would choose Scraggy. Noibat's stats are way too low for major battles, while Scraggy can handle its own until it evolves. While it has low Speed, its stats and coverage make up for it.
I hope I've helped!