Hello,
Just down the coast from me, (I am based at Lagos marina). I visited Portimao and had a look before plumping for Lagos (I hasten to add only because it was closer to my home). Plenty of room between pontoons, nearby marine facilities (e.g. engine servicing). Staff helpful, a little way from the centre of town, but seaway access only a few minutes from the marina. Hotel and resturants nearby.
We chose Lagos over Portimao in 2006/7. Lagos is a much nicer marina, and there is much more going on. A short walk from town, whereas Portimao marina is miles from town.
Portimão is a long way from town centre and if you have to drive there is an awful one way system where you can get to town in 5 mins and to return is 15 mins.
It is cleaner than Lagos and larger than Albufeira.
Portimão is a long way from professional boat sevices and your nearest would be at Lagos or Albufeira.
For repairs Portimão is a do it yourself marina.
Watch out for the people in orange "T" shirts they are dangerous for the health of your boat.
We visited quite a few times, nice village opposite called Ferigoda (spelling) a short dinghy ride or there is a small water taxi that doubles as a rescue boat. Proper old Portugeuse village, fantastic fish resteraunts all around the square with a couple on the quay cooking on an open grill outside the day's local catch.
Good anchorage to the East with a nice beach and a couple of nice bistro type places.
Good beach on the west side, as said long walk into town.
Hotel complex to the North has a pool and a bar that will let you sneak into.