As an owner of both, I'd say get the '13.
+'s to '13-
Much better heater and a way to turn it off, although living in LA heater might not be that big of a deal.
SOC% display, no SOC display on '12, only more woefully inaccurate GOM.
Much nicer seat fabric, well unless you like velvet smooth very light seats of the '12 that show EVERYTHING!
Double the speed L2 charging, shop for 1hr gain 30% battery, it's about half on the '12
Tad less storage room in the rear due to location of charger
4th button on FOB to open charge port door, the '12 is mechanical and must be pulled inside the car
More regen, although this may be because my '12 has 10 bars and my '13 is full at 12.
No IRRITATING nag screen EVERYTIME you start the car for NAV and no need to double shift to get into ECO mode
+'s to '12
More features such as Cruise Control, ability to stream audio via Bluetooth, photochromatic rear view mirror, build in universal garage door opener on rear view mirror, rear hatch storage cover/shelf,
A bit peppier, could be a benefit for some although I prefer not
Select magnesium body panels, no rust?? although in LA rust probably isn't an issue
Mag rims, although I prefer steel for less air leaks
Electric parking break, I never use it so I could care less, others may feel differently
Slightly better sounding stereo, comparing base stereo to base stereo
NAV if you use it, I use my phone
Larger backup camera/functions screen, backup screen also has nicer lines that move when you turn the wheel
Auto on headlights and brighter LEDs, no LEDs on '13S
2012 SL purchased used 2/'16
2013 S w/QC purchased new
Juicebox Premium 60a L1/L2 EVSE, Ebusbar 16a L1/L2 EVSE
'12 EVSEupgrade'd 20a L1/L2 EVSE, '13 EVSEupgrade'd adjustable 6-20a L2, 6-13a L1 EVSE
Zencar 13, 20, 30a L1/L2 portable EVSE
GE Durastation 30a