We were just on this cruise in June. Embarkation at Civitavecchia was a breeze. We had a listed embarkation time of 1:30, but based on other comments I read, we arrived at 10:15 AM. The line opened at 10:30 AM, and we were on the ship in less than 15 minutes. We had lunch at the Windjammer so I can't answer your question on other options. The ship was relatively quiet.
At Barcelona, look for the Returning Guests sign, and you can bypass all the others to get right on the ship.
One other thing to note, the Royal App did not work for us boarding in Civitavecchia. We could