PC Fan Suggestions

Hello, I recently received a fan splitter so I can use more than 1 fan in my PC. I currently have a CPU fan and 2 Case fans running.

I was mostly wondering which case fans would people generally consider to be more important if any? The rear fan (right next to the CPU fan), side panel fan, or front fan? I can use 2 of those 3 and want the best possible air flow.

I'm using the CPU fan, side panel, and front fan right now (since my CPU fan is so close to my rear fan anyway) and was wondering if there's a better combination or if it really doesn't matter (which I'm pretty sure it doesn't, but hey, I'm curious)

Thanks!