I am a major fan of Merida/Progreso area.
Merida is a wonderful City as others have posted.
I have never been there in the summer. It is quite hot. So, I am told that everyone from Merida is at the beach. I have only been there in the winter when the area is deserted. But, the beach area is a retreat for the Meridians to escape the heat of the inland city. So, it become a bustling area.
The rental offer in Telchac Puerto looks nice. However, I have been to Telchac in the winter when it is deserted. It is a quiet village that I would say is fairly isolated.
In the winters I have stayed at a home between Telchac and Progreso and always enjoy the area. Its true that the beaches are not the Caribean beaches. But, I have been told that in the summer they are very nice and clear.
I've taken my kids there over the years from the time they were 11 and 13 to 15 and didn't care to go anymore. However, they always enjoyed the trips even without tv or computers. I do continue to go there. And, now that my oldest is 21, she's wants to go again.
I'm not a fan of "all inclusive". They just don't appeal to me. But, maybe it would suit your needs. That said, I've never stayed at one. There is one between Progreso and Telchac. I had friends stay there and I ate one meal there. I was unimpressed with the food. And, my friends were not happy with the place in general. Its isolated. And, without a car, you're stuck with whatever they have to offer. And, this will be true of any AI to some extent. So, if you chose to go AI route, do your homework and check around for reviews.