good question
the 2008-10 had the same facelift.
2009 300C 5.7L hemi gained 19hp and some extra TQs over the prior year due to variable valve timing.
The 2010 300C 5.7L, according to Edumonds.com:
The V8-powered 2010 Chrysler 300C receives standard keyless entry/ignition
and rear parking sensors, and all 300 models get standard side curtain airbags;
however, front-seat-mounted side airbags are no longer available.
So a few extra goodies in the 2010.
I'd lean 2010, as I want that push button start
