Fedora 14 isn't based on a development branch of anything since it went final. LMDE is. Testing or Sid based distros aren't for everyone and they will likely break sometimes. So, if you don't like fixing things sometimes or waiting for the repos to fix them, they're probably not the best choice. Neither Sid or Testing are intended for production use.
In fact I would say that if you want a nonbuntu out of the box distro that is less prone to breakage, Fedora, PCLOS or something like Mepis are excellent choices. personally I would recommend PCLOS - Texstar is a freaking god and they have a great community. If there ever is a prob, he fixes things super fast (sometimes within hours) and they have the best implementation of KDE I've ever used. Needless to say, Julia is also an excellent choice. Clem and the team do a nice job cleaning *buntu up and it's a little easier for them to fix things with. With LMDE they are pretty much at the mercy of the Debian repos.
Personally I think LMDE is a nice fork of Debian, especially after tweaking things a bit. But users looking for an out of the box, low maintenance distro may not. (just wait a couple of weeks, when the testing repos unfreeze, things might get interesting lol.)from the Mint blog:
4. How does LMDE compare to the Ubuntu-based editions?
* You don’t need to ever re-install the system. New versions of software and updates are continuously brought to you.
* It’s faster and more responsive than Ubuntu-based editions.
* Although it’s using Romeo for unstable packages, LMDE continuously changes as it receives updates and new software. Compared to a frozen version of Linux Mint which changes very little once it’s publicly released, it’s not as stable. Things are likely to break more often but fixes can also come quicker. For this reason, LMDE requires a deeper knowledge and experience with Linux, dpkg and APT.
* Debian is a less user-friendly/desktop-ready base than Ubuntu. Expect some rough edges.