We booked with PCL only because of the short time there. Otherwise would have taken the train on our own. Though later I heard at the airport; that some passengers did go on the train but it was a bit risky.
We chose the Paris on your own - prety pricey - but we did not know if and when we'd get a chance to go back to Paris.
The bus/coach ride took around 2.5 hours - not bad - we had around 4 1/2 to 4.75 hours on our own. However, the attractions are opposites of each other so if you have trouble walking - it will be a strain on you. Trust me.
I had purchased online tickets for the Eiffel Tower and chose the 12:30 time giving us time for "problems" on the way. First mistake: We were at the Tower at 11:25 and had to wait for the scheduled time we chose. So, if you are in good health and can walk briskly; it probably is safe for you to book your online lift/stairs tickets for the 11:30am - if available - this way you safe an hour for the Arch and the Louvre.
We purchased from the official website. Make sure you choose correctly!! I picked the 2nd level only thinking it was for the 3rd level also and was dissappointed. Though it turned out OK since the lines were pretty deep for the last level and with having lost an hour already; well you get the picture.
All in all, it was amazing to see the Tower; the Louvre; and a glimpse of the Arch. One warning - there are signs all over about pickpockets. I did not trust to give my camera for anyone to take a pic of me and my husband; :( Also, many of the people there you could not make out if they were tourists or locals So just beware. Best thing is look out for others from the ship and then take the pics.