Linux Mint uses the LTS version of Ubuntu so the “base” gets updates about every 2 years just like Debian. As such, both are going to be “about as new” as each other (emphasis on “about”).

Ubuntu LTS pushed a bad kernel update where the headers were not available for a while. This meant that anyone using additional drivers (like I was for my networking) would have the kernel fail to install and then the operating system kernel panic when you boot up the next time. That is surprisingly “not stable”…

Debian, which will update about the same amount, has not pushed a bad update like that as far as I recall. That being said, I have had less experience with Debian.

The Linux Mint team seems to publish packages to LMDE so that it will have similar features to Ubuntu (like codec support) so you won’t be missing that by using the Debian base. That being said, minor differences were present (such as guest mode missing compared with the Ubuntu base). Also, Ubuntu may have support for additional hardware in case you need that sort of stuff and will have HWE kernels that will support newer hardware than Debian.

Still, if LMDE works for you then it is more likely to keep working in a boring and predictable manner. If you are using the Ubuntu base, you may have a random update mess things up which will require you to do some troubleshooting. Ideally, you won’t notice much of a difference between the two though.

The big one is no Snaps. You can get them, but I prefer flatpaks which I use on LMDE.