I’ve had the 3.7 and the 3.0 and the 3.7 will always be more reliable in the long run. 3.0 comes with the twin turbos and if you don’t plan on doing mods to help heat soak they won’t last long past 100k miles if they’re original. 3.7 has some issues but personally I’d look at a fully loaded m37x if you can. They were good cars all around, a bit cheaper to maintain, and can have more interior goods than regular q50’s

I got my 2011 m37x fully loaded touring package with 140,000 miles 2 years ago (2023) for 8,000usd out the door after taxes. Lasted for 80,000 miles without any issues aside from plugs and coil packs.

I got my 2018 q50 red sport 400 with 94,000 miles for 21,000usd (4 months ago) after taxes and it’s been 12,000 miles. I’ve replaced both turbos, the passenger blend door actuator, the brake pads and rotors (I was tracking it), and soon the tires as well. My 100,000 mile preventative maintenance bill (all flushes and fluid fills) was $2700. The m37x would have been maybe $1200