If you were buying a new laptop and had to choose between more RAM or a more advanced CPU, which would you choose?

i5 isn't more advanced than i7 it just performs better in simultaneous tasks. Arguably in many/most cases an i5 is better because counterintuitively it performs better on a single task, consumes/heats a bit less, etc.

That said RAM is (usually) upgradable and the CPU not, so the focus should be on the latter still