On my escort, I ran 5w30 mobil 1 synthetic, it was great.
Of course, I eventually learned that the motor LOVED thin oil. I began cutting the oil with a quart of 0w30 mobil 1 synthetic on each oil change (4 quarts of 5w30 and one quart of 0w30 seemed to work best) It ran sooo smooth and quiet, and regular oil changes revealed no added wear. it was an aluminum engine as well.
You should change your filter at every oil change, true, some filters are meant to be run past 3K miles, but it's a small investment to make for engine longevity.
I've been running 5w30 dinosaur juice in my 2ZZ, starting next oil change, I will be switching over to synthetic, since it's all loosened up now. I would cut the oil on this car as well, but I'm not sure how the engine will take it, considering I push the car hard occasionally; I'd rather sacrifice flow for some added protection anyways.
Natural oil and synthetic can be switched out with no ill-effects. the bit about not switching because it'll hurt your engine is a myth. both petroleum-based and synthetic oil are made to do the same thing; lubricate moving parts. some synthetics actually do the better job.
blends (half synthetic/half petroleum) are rather new, I don't think they'll hurt anything, but they aren't that bennificial either. You might as well go full synthetic rather than buy half and half to save a couple bucks, but that's just my opinion.
I prefer Mobil 1 synthetic. Other brands are pretty good, but past experience and others opinions sesm to confirm this. If you go with a natural oil, you can't do better then castrol, it's the shiznit! and we use it in everything, from bikes to the streetrods in my bro's garage. They add castor oil to their formulations, and this stuff is great for reducing friction and wear. Some dedicated race cars just run straight castor oil exclusively, so it's not just hype. Hands down, Castrol is awesome if you want to run au-natural.
hope this helps