There are so many choices but none of them is perfect, in my opinion, which I regret a lot ! Here's my personal take on this (after using each of them for months) :
- KDE is amazing but never perfectly stabilized and tends to be messy (although there are efforts to make it simpler). I always, after a couple of months, drop it because some non-obvious but still important stuff is broken.
- Unity is getting mature, brings very good ideas, but if you don't want to use the keyboard a lot, some basic actions get ridiculously difficult to perform. I'm extremely frustrated when I use this one. (sliders, global menu, dash I cannot stand, window switching very painful IMHO)
- Gnome Shell is pretty impressive and extendable, but, they pushed the simplification so much in some areas, some basic stuff cannot be done (without tweaking) and you lose time for instance when switching windows. I feel they are forcing a specific way to use it, which I only moderately like. I am VERY puzzled by new stuff they are introducing (the "one button global menu"), the "centralized" documents app, the fact you have to hit the top-left corner for everything, etc.
- Gnome Fallback lacks some polishing and doesn't benefit from many new Gnome Shell technologies which makes it a 2nd or even 3rd class citizen.
- MATE : I don't know what to think, I wonder what the long term plans are.
- Cinnamon kind of looks like it's yet another duplicate effort and the fact they fork Gnome Shell instead of extending it upsets me. But I have too see what Clem's long term vision is. At least it's Gnome 2 modernized. As a result it's what I'm using, at the moment, but it may change.
Regarding composition on my medium-end nvidia setup, the observations are similar (everything is quite good but nothing 100% satisfactory) :
- kwin : when disabling a specific option, it's extremely fast, complete and smooth (otherwise it's jerky). But tends to be demanding / not give good results on all setups. Games are not smooth unless fullscreen compositing is disabled.
- compiz : OK in most cases. Not really smooth, settings are such a mess, but at least it's consistent...
- mutter : butter smooth, but it seems, according to benchmarks, that you lose some FPS in games. Dunno if it's still true.
Well, this is just my humble *own experience*, and I'm sure, many of us will draw different conclusions....
This being said : I appreciate, to some extent, all of them. My point is : so many choices, none of them being really satisfactory. Which makes me sad
WHAT A LOSS OF TIME switching distros and environments, what a loss of time contributing to X different yet similar projects. IMHO. If I weren't a free software advocate, this is probably the reason why I would get frustrated and drop Linux. But I won't, I love Linux nevertheless