Your choices aren't omni vs. first-person. Why not use third-person limited? In that, you can change POVs at scene and chapter breaks, so you're not limited to a single POV.

I also don't think that a single POV limits the world-building, beyond that the audience can only experience the parts of the world that the POV character experiences (or hear about parts the character knows about). If you mean world-building in the sense that you want to show what's going on in different parts of the world that your POV character couldn't possibly know, then, yes, you're limited. But, then, are those parts really needed if they don't affect your POV character's story? Or are you able to have them affect it in a way you hadn't originally planned on.

(I would suggest, in the future, not bumping threads that are this old. If it's been 8 years since the topic was last mentioned, you're probably good to start a fresh thread)