If you change the oil less than every 5000 miles, and you are not towing a trailer or doing some other severe service, then a mineral (regular) oil should be more than adequate. Use exactly the grade that your owner's manual recommends for your temperature range. The synthetic is probably better, but the difference in wear characteristics are unlikely to be significant (i.e., other components in the car will disintegrate or fail long before the engine will due to the difference in mineral versus synthetic oil). I recommend the stock Volvo oil filters. Enjoy!