Synthetic or conventional?

Change it yourself or have it done?

Advantages and disadvantages..... etc.

Here`s my list:
2000 Pontiac T/A LS1 V8: Mobile 1 Synthetic 10-30
2006 Pontiac Grand Prix GTP 3800 V6 S/C: Quaker State 10-40 Conventional
1982 Chevrolet Corvette 350 V8: Castrol GTX 10-50 High Mileage

Wix Filters in all vehicles; I change it myself every 3000:cornut:....

What are you using?????