In terms of promotions, I don't see a big difference as I saw both platforms are being used. I don't see yet an accurate stats wherein one is more effective over one and vice-versa so overall, our judgement is based on our own view.

But in terms of an organized community, Discord > Telegram as unlike in Telegram where all queries are discussed and mixed in a single group, Discord can create multiple channels out from a single server so that discussion is sorted out e.g there is a separate room for discussion, contest, etc.

And might be a hassle for anybody or not comfortable when Telegram is asking mobile number in account creation. I will disregard scam thing as promoters and marketers will target audience no matter how worst the platform is as long as it's a big community and has lots of registered users.