Are you on a tight schedule? Do you like to explore on your own? Do you prefer learning a lot of details about a site, or just want an overview?
I usually prefer a completely guided tour when I have limited time in a location. Often the guides will obtain entrance tickets in advance, or can go through the tour group line, which might be much shorter.
I do try to preview maps, highlights, and information of a site before I arrive, so I have a general understanding in advance.
We were just in London this Summer, and visited the Tower without a guide, and were able to wander alone by ourselves for more than four hours, enjoying all the different sights. Yet when we went to Westminster Abbey for a few hours, it just felt overwhelming to locate all the different tombs, and we were lucky enough to connect with one of the volunteers inside who acted as a de facto tour guide for us. (Yes, I was in both places before, but decades ago.)
I am okay with audioguide devices, but not my favorite, especially as all information is prerecorded.
I do have to say, even though I am completely bilingual in Spanish and can read all the signs, I often enjoy the tour guides because they add their own unique perspectives, and can usually answer our specific questions of interest. We really enjoy history, and want to know a lot of details. The guides also usually know where specific items are located on a property and can find them quickly, and can navigate through crowds.
The ideal mix would be to first take a tour, and then afterwards have some free time to explore on your own.
Have a wonderful visit!