I am sure we can get several opinions out of this topic. It’s one of those things that you either like or don't, usually depending upon how traditional the instrument and your tastes are. Traditional players have said to me why? Why would you cut a hole in the side of a perfectly good guitar when guitar design has been worked out and handed down for at least several hundred years. While there is certainly some legitimacy to the comment great guitars sound just that, great. Let’s just take a little rabbit trail for a moment and look at for example bracing. We won’t go too far back though. Early instruments give us ladder bracing of various types from northern and southern Europe. Which, in their own right have a sound that is preferred in particular styles of playing. Then comes along the rogue builder and for several reasons ( most notably larger steel string guitars) brings in the X brace system. I am sure that along the way traditional builders of the day would be saying hey, that kind of bracing affects this or that negatively or adds additional weight and so on. Here is one for the classical group (Kasha Design). Let us not forget double X bracing and so on. All this to say that guitar design changes happen for a myriad of reasons, Some by design some by happenstance. I cannot speak for others however Sound ports for me, was a happenstance scenario.
While working in my repair shop one fine day a customer comes in with a panic look on his face. His Fishman Prefix system was blown and he had a show to do in a couple of hours. Being a small enough shop not to stock a lot of high priced gear I offered a possible solution. Take the Prefix system out of one of my guitars. He gladly accepted my suggestion. So I removed the unit from my guitar and put the guitar back in its case. Of course I intended to replace the unit a.s.a.p. but as things go it was quite some time before I actually replaced it. Sometime later I had occasion to pull the guitar out and noodle around with it with this giant hole in the side. I was amazed how much different I thought the guitar sounded. It was louder to me for sure but it was more than that there were subtle tones that were available to my ears that were not there prior to the hole (subjectively I thought). I covered the hole and uncovered the hole quite a bit over the next several weeks and was convinced that the guitar was different enough for me to build a few with a port in the side of the upper bout. Eventually I did. There are some photos on my pinterest in the acoustic guitar folder. I originally made them to keep yet when I was in the process of selling other guitars the original sample ported guitar was selected over other similar models. Thos one was a roughly 2" "S" shaped port. The funny thing is that customers that bought the small ported guitars were originally unaware that the ports were in the guitar when they picked them up to play. Their comments to me were “wow there is something different about this guitar”. I actually had to point out that the guitar had a sound port. On a couple of occasions the guitar was not sold. Even though the customer thought the sound was a bit better. There was a stigma associated with the hole in general and they selected a different instrument without the port fortunately I sometimes have a couple of selections for sale at the same time that are not custom orders ( compulsive building syndrome ).
All this to say the sound of a particular guitar is a very subjective thing. Sound port, no sound port you be the judge. For those that can and do have several guitars IMHO sound ports are a good thing, and when you are sitting around playing that sweet acoustic, the sound port would serve you well. Even in a room with other acoustic players where you typically would be struggling to hear you own guitar the sound port would serve you well. Now once you plug into that amp all bets are off. The advantage of the port is primarily to you as a player, not the audience. That the difference in the guitar sound could not be discerned by listening to it from across the room is a good thing, it means that it is not degrading the overall concert potential. Since that early happenstance sever guitars have been ordered with sound ports some of them more re decrotive then others. i have done flowers, initials, oval, round, and others. The bottom line for me is that in my stash of guitars I certainly have one with a sound port. My little brazilian parlor sounds fantastic with the port, anyone who has ever played it agrees that the port made a sweet subtle difference and improvement to the player.