Which distro is more stable and reduce RAM consume than Ubuntu 17.10? Your thoughts

For stability, Debian is known for being stable: the drawback is that you won't have the most recent updates.
RAM is mostly impacted by your desktop environment: XFCE or LXDE are light. If you want to spare even more, try a simple windows manager like i3

To really save on RAM try Arch Linux or LFS. Coupled with a simple WM such as i3wm, awesome, xmonad or even openbox, LXDE, FXCE. Some of which were suggested by @MeanStreet.

Choose wisely with your applications you run, too. Use Midori, and the terminal as much as possible.

These recommendations might be a bit far, but I'm not really sure how much RAM you want to save.

If you want an easier installation, try Linux Mint or Ubuntu MATE :)

Do a quick google search and you'll find some goodies! :D