Depends on what his driving needs are. If he spends more time in the car and on the highway then the 9-3SS may be a good call, its a nice place to spend miles.
My cousin has a 2002 WRX that I drive all the time and its a great car. The 2002 had some trany problems and his WRX with less miles has already gone through a clutch and the shifting feels a bit worn. That may just be him though and the car lived 20,000 miles in SLC (hills.) Fuel economy blows. I recently put 18,000 miles on a 2005 9-2x (subaru 2.5rs) in 5 months and I didn't die but the noise and the seats got to me. Its a great car but for comfort and distance the 9-3 wins hands down.
If he has a long commute and/or values comfort the 9-3 is great (also amazing MPG).
If he only needs the car for short trips or really likes a more raw feel the WRX wins.
BTW Here's a shameless plug for my 9-3 that is for sale in North Jersey.