Have a look at the thread from the beginning. Basically though, *any* API SL 5W-30 oil changed at 3750 mile intervals (or up to 7500 mile intervals depending on your situation) will be adequate for a motor life of 60,001 miles.
Beyond that, you have too many choices to list really.
If your seals have deteriorated a good synthetic will be coming out of them within 10K miles of switching IMO. If your seals are fine, a good synthetic will keep them that way as long as possible.
A typical conventional oil will probably have a lower flash point and volatility than a good synthetic, and will tend to respond to shearing forces not quite as well as a good synthetic. This trend will get more pronounced as the oil change interval gets larger, meaning that if you're going to change oil every 1,000 miles use any API SL oil (the cheapest) but if you want to go beyond 5,000 mile drain intervals take a close look at high quality synthetics, again IMO.
There are many synthetic blends that are quite good, and many full synthetics that are not synthetic at all. To figure all this out you can either use trial and error or look for used oil analysis data from owners with the same vehicle you have. Subaru motors seem to be setting a trend for being easy on their oil, though they might snack on a little now and then depending on the area, use, and the type of oil.
Find the link to the Subaru used oil analysis spreadsheet form, I think it's on this thread and I know I posted it. You'll end up with info from a variety of vehicles and a variety of oils, and you'll see how each faired so you can make up your mind.
I switched to synth at 12K. Others have done it sooner, some have done it later, some never go to synth. I just changed oil yesterday, after another 5,000 mile drain interval. I used M1 10W-30 again, a fresh drain plug crush washer, and a Purolator filter that I pre-filled with oil before installing. I then went extra-anal-retentive and gave the ignition key two or three minute turns so that the motor would turn over without catching. Then when it finally caught on the oil pressure light *never* lit. This was a useless psycho thing to do at 12 am on a weekday, but I did it...