Cinnamon and MATE you should compare on Linux Mint 14 or above version (so Cinnamon 1.6 or newer), as the Cinnamon version (1.4) that shipped with Linux Mint 13 still had a ton of cruft from Gnome Shell to be removed--and all that cruft made it resource heavy and slow to load. Cinnamon 1.6 version cut all that Gnome Shell cruft away and that has immensely improved Cinnamon, easily outpacing MATE on all fronts.
But there may be other factors, as some users like you state that for them MATE is faster to load than Cinnamon. Is that on a clean install I ask, or one slowed down by applets
Some users dug into that a while ago and some older applets can really drag down Cinnamon performance (these aren't installed by default). Regardless, perhaps your graphics card driver plays a part here also. I use Intel graphics.
Anyway, Xfce might boot faster but I think you'll have to do some more tweaking to get it to boot significantly faster (so that you can say for sure it's faster, without looking at a clock). From the default loaded services there are a bunch you can disable. Service not loaded = less programs to load during boot. For fun I had a Arch Linux install with just the minimum Xfce desktop installation. It booted in less than a second