Perhaps it would help if you knew the differences between the Mears Shuttle and a town car.
If you are using Mears:
You will get your baggage and go to the Mears area on the lower level of the airport. Present your vouchers, and you will be told to wait for the next bus. (Depending upon the demand at the time you arrive, it could be a full sized bus or a mini-bus that seats about 15.)
Again, depending upon the crowds at the time you check-in, you could wait anywhere from 10 minutes to an hour. There is no way to predict this, and it is totally the luck of the draw.
Because Mears is mass transportation, you will probably drop people off at other resorts before you get to POR.
The cost for this, round trip is around $30 per person.
If you are using a towncar:
You will get your baggage. Waiting for you at the baggage carousel will be a towncar driver holding a sign with your name on it. The driver will meet you at the curb and put your luggage in the trunk of the car.
If you have requested it ahead of time, you can make a stop at a grocery store for snacks, film, water, etc. before you get to the resort.
The towncar services will provide car seats, if necessary, and if requested ahead of time.
There will be just your party in the car, so you drive directly to POR.
With a tip, it is around $100 ($80 for the ride and $10 tip each way). This price is for the CAR, (not per person) which will seat 4 comfortably.
There is nothing wrong with Mears. It is just a less personal form of ground transportation. Many people prefer the privacy and direct service of a towncar.