I found Gentoo more helpful than LFS because with LFS you compile about 80 packages from source one at a time but you don’t learn too much about the packages.
LFS gave me much more awareness of what packages actually come with a Linux install but Gentoo taught me more about configuring and booting a Linux system.
Although I’d definitely recommend both to anyone wanting to learn. I’d do Gentoo first then LFS.
Edit: LFS is also a masterclass in cross compiling so if that’s something you’re curious about LFS is the way to go.