I've tried both on a dinosaur laptop (had a single core Intel Celeron CPU, 512MB RAM... like absolute dinosaur). Lubuntu doesn't seem well supported at all, it looks like an operating system made for a RasPi (ugly and a pain in the ass find files and programs because there was no search bar in the menu) and it ran SLOWER than the more modern feeling Linux Lite. Is there something I'm missing or is Lubuntu just terrible?