I currently own a pair of Titans, they are down the basement gathering dust, IF I ever go to 7.1 they can be the back speakers.
I have heard the M3tis and to my ears they were a "bigger" sounding speaker. If I had to choose I'd go with the Axioms even though Atoms/Titans are also good small speakers.
My evaluation is totally unscientific. The speakers weren't in the same city never mind the same room when I heard them
You also may want to consider future purchases when making your decision if having all speakers the same brand is important to you.