which MCU suits me best ....

Will you need to use an operating system such as Linux?  Or would a simpler OS (such as TI-RTOS or other small RTOS) be good enough?

If you need a lot of processing power and/or Linux, I would recommend Cortex-A series.  If all you are doing is gathering data and just sending it or saving it somewhere with very little processing, then the M series may be good enough.

If you're not sure, probably go with the A series even if it's more powerful than you need.  Better to have too much than too little when you don't know in the beginning.

You may even be interested in playing with the Beagle Bone Black (http://www.ti.com/tool/beaglebk),  It's pretty cheap, has Linux, and runs on Cortex-A8 processor.

@ particle obsessed poster,

Some way/how, "Hydrogen fuel cell & perpetual motion" escaped o.p.'s (well considered) laundry list...

Does not the nature - and construction of such a post "signal" poster's (likely) background/resource/reality?
Coast guard has (somehow) certified my sailing skills - yet my sails descend when Pacific growls - or coast becomes, "too distant..."

Real world has nasty ability/habit of "culling the herd." Some match of, "ability/background/resource" to desire should ping one's radar...

KISS (clearly) deserves some consideration - "Reactor design for beginners" has yet to march up best seller list...   (perhaps for good reason)