I've been using Pop! OS on my white Macbook4,1 and I'm quite impressed with its speed and UI. I had to download a small program to mod the ISO to get it to install, but this site tells you how to mod pretty much any 64-bit linux distro iso to boot and install on 32-bit EFI Macs- Linux DVD images (and how-to) for 32-bit EFI Macs (late 2006 models)