Do you guys prefer going directly to the 4S dealership for repairs, or do you tend to buy parts yourself and find a repair shop?

You can go to a specialized repair shop after the warranty expires. Make sure it's a shop that focuses on specific brands, not a general repair shop that handles all types of vehicles.

For general parts replacement, it's better to trust the quality of 4S shops. For other maintenance like oils and fluids, you can opt for outside repair shops.