Been covered heaps of time, try searching.

Generally people suggest a semi-synthetic 10W40 oil. Apparently subaru engines don't like fully synthetic and causes blow-by/glazed bores from prolonged use, and then there's those that argue against this.

Change intervals+filters are more important as long it's a 10W40 oil. Only oil I've heard from most people to stay away from and is from a well known brand is castrol magnatec.