All I would say that it should meet the dexos1 Gen 2 and/or SN Plus standards and be 5W30 or "heavier".
I guess I have used more M1 5W30 than anything else in my FA20DIT. M1 5W30 ESP was a big favorite on subaruforester.org for a while and I used it for a couple of changes, but now there are two versions of that and I don't know which is which.
If you go on NASIOC, you will surely get a bunch of Rotella 5W40 recommendations...
BTW, I'm assuming this is not an STI?
I loved PUP but switched to Mobil 1 EP due to availability. Ran EP for a while then made the switch to amsoil, really like amsoil and it's served me well. I recommend using the oil that catches your eye the most
Recommended oil for your car is a conventional 5W-30. dexos1 or synthetic is not required. 5W-40 is not recommended by Subaru.
I would use a synthetic 5W-30 though, as these days synthetic is very cheap and you get all the extra benefits. Mobil 1 would probably be my first choice but they are all good.
I own and track a 2015 WRX. I use Castrol 0W-40 A3/B4 mostly, but have also used Shell Rotella T6 5W40 and Mobil 1 FS 0W40. Direct injection and track use cause the oil to shear down to the higher end of of a 30 weight. It burns no oil and gets 32 mpg at 75 mph.
It is a great car and at 28k miles, has not been back to the dealer once.