I don't know what year we're talking about, but I'd just do the whole strut. I have done both in the past for different vehicles and I prefer to just replace the whole unit.
Either strut replacement procedure can be done but spring+strut combos are easier and safer for the home mechanic. For a little more $$ ready-to-install spring+strut combos are readily available. If your Pilot is high mileage the springs, bearing plates etc. will be worn and should also be inspected/replaced.