I have been switching back and forth between Unity, Gnome-shell and cinnamon for over a year now, trying to find the one I like best.
Unity, has actually become quite ok with the latest versions. I think it's a bit too mac fanboy for my taste, but I could see myself using it as a default DE. The problem with it is that it is a huge, slow, bloaty abomination. I recently got a HP 655 AMD fusion laptop, and unity does not run well on it. It might be driver issues or something, but windows 8 ran better that unity.
Gnome-shell is technically quite good, it's a little slow as well, but much better than Unity. The problem with it is that it's not quite all there. You really need a lot of extensions to make it good, and then it becomes buggy and awkward.
Cinnamon is basically a gnome 3 version of gnome-panel from gnome2. It's very basic, but works quite well. But for some reason I always leave it for something else. It might be the lots of small bugs and glitches it has, or that the Ubuntu version is not really that finished (and Linux Mint is just a version of Ubuntu with less functionallity).
Well, this brings me to the point of my post. I decided to switch it up completely. I first decided to try Xfce. I have used Xfce quite a lot on media machines and other single purpose boxes and have liked it for that purpose. I didn't however last very long with my test on my laptop. Firstly, i really miss the search box directly in the menu, I basically use that on all my main systems. Secondly, I'm sure Xfce could be a really powerful DE, if you would put in a lot of time tweaking it, but as the defaults are very badly suited for laptop use (power and screen management comes to mind) I decided to continue my search. I even tried some non Ubuntu based distros, but the lack of apt-get is too much of a culture shock.
So I had to take the bull by its horns and try the only sane choice I had left: KDE. You might ask yourself, why not try it earlier? I'm a bit ashamed to admit that the reason is quite simple. I really, really don't like the look of KDE. It uses over the top graphical elements that look like they where designed by colour blind programmers. The UI design is quite unintuitive and really strange. I have however started to grasp the whole point with it after two days of use. I have actually tried Kubuntu before, but it was sometimes in the Dapper days, and it was quite buggy then.
Anyway, I have decided to try Kubuntu for 2 months and see how I like it. So I shall try to report back the first of November to let you know if I will continue my search or stay with KDE. So far after getting used to the vomit-inducing graphics, it actually seems pretty good.
We shall see....