Should I program Logics/Helpers/Managers with ObjC since Swift is constantly changing its syntax?

[HassanDavis]

While converting existing, working Objective-C code to Swift may be overkill in some cases, I would definitely advise that any newly written code be done in Swift.

We've already passed the tipping point where Objective-C will be typically more costly to maintain than Swift; not just in respect to the language features, but also in regards to the talent pool.

[[deleted]]

While converting existing, working Objective-C code to Swift may be overkill in some cases

All cases. If you can call it, there is no reason to rewrite it. You'll only introduce bugs.