My first distro was Mandrake. I switched full time around the very first Ubuntu LTS release (because damn winmodems).
Nowadays I use Kubuntu / Linux Mint KDE, mostly because I like KDE and I've been stuck with Ubuntu derivatives for ages, hence I'm quite familiar with it. However, I strongly disagree with Canonical's direction and recent (i.e. last few years) actions and the core system is horribly rotten; I experience trouble with hardware support, that don't exist elsewhere, packages in official repos are broken out of the box, etc.
I'd be already running Fedora, if Anaconda wasn't so horrible and the fedora.next software management (plus SAT solver for yum) was in place.
A year later and I've completely abandoned Fedora, because the project apparently puts more focus into politically correct rubbish than solving actual technical issues. I prefer a working system to a system developed with contributions from elderly African American transgender lesbians—at the risk of being eaten alive by certain redhatters. For example, my webcam has gone from partially usable to unusable in three releases; surprisingly, that's one of the things that currently actually work perfectly in Ubuntu derivatives.
I'm only a bit worried about the development cycle of Kubuntu. Sitting on LTS means I'm sometimes stuck with outdated software, while the upstream actually solves issues (the case of my webcam). OTOH, latest and greatest releases bring other kinds of issues (such as broken default configuration for serial Wacom digitizers, that prohibits them from being detected correctly, or rather at all). Unfortunately, Debian (a) doesn't even have PPAs with the latest upstream software, and (b) downstream isn't any better.
In particular, I'm on the fence about 15.04. I wouldn't have to compile Emacs 24.4 by myself (yay), but I'm still wary of the "KDE 5". Not because I expect a KDE4-like "disaster", but I have a very specific workflow that makes use of some of the weirdest settings in KWin, and some of them may not be implemented… yet?
There's still Gentoo/Funtoo/whatever in the air, but I talked to some power users in autumn, and they hated on software written Haskell, because it's supposedly a PITA to compile and/or manage. That might be a deal breaker for me, because I tend to use quite a lot of data-processing tools in all sorts of very high-level languages.
/rant