Mutation X is basically a pre-modified Tobh... which is an excellent RDA... I modified mine for more airflow. The Mute X is already done and ready to go.
I've got no experience with the Plume, but there are many who like that one as well...
I'm personally not a huge fan of the Stingray (and I'll prolly get slammed for saying so), there are just too many of them out there for me... but it is a solid mod.
My favorite mod at the moment is my carbon fiber Knight mod... solid copper with a carbon fiber sleeve... less to tarnish... also, whatever copper blend they use seems to hardly tarnish at all, anyway.
Either way... you can't go wrong with what you're looking at... I assume you already have meters and know what's what when it comes to battery safety and Ohm's Law... if not, I can get ya some info on all that as well...