The powerful part of Processing is not the IDE it provides, but rather the way it wraps both core Java functionality and significant third party libraries to present a single “API” of sorts for the programmer who doesn’t have the knowledge or skills and experience to deal with the underlying complexity directly.
The IDE itself a solid enough bit of software and it does a decent job, but there are definitely better tools.
Personally I like Eclipse a lot, although
it was my first experience with a good IDE, but that doesn’t make it or any other choice the right one for you. I’ve also used PyCharm (which is also made by the same company as IntelliJ IDEA). While it seemed like a perfectly serviceable IDE, using it felt like a hindrance to me.
I think Eclipse works fine for working with Java (and Processing, which is kind of a subset), but no better probably than any other IDE in the latter respect. If you’d prefer IDEA then go with that.
Which IDE you use isn’t that important, beyond personal preference, unless you specifically need a feature that some of them don’t have.