I think Nim and Zig target very different audiences and have very different goals. Nim is about being a big, powerful language with lots of features, so that you have the freedom to use it the way you want, e.g. there is OOP with methods, but it's completely optional. Zig is explicitly against that, even on the homepage you can see: "No hidden control flow. No hidden memory allocations. No preprocessor, no macros.". While memory management in Nim by default is completely automatic, and templates/macros are quite common.

It makes much more sense to compare Nim to, say, Swift, D, or other modern compiled languages with lots of syntax sugar.

You may consider Nim as a sort of "compiled Python" with some Pascal influences.

https://nimble.directory/ I'd pick Nim if my concern is general app development, not specifically system programming.