Depends what you are looking for. Titicaca, or Copacabana anyway is very touristy. Sajama is almost empty and in my opinion much more beautiful, it also has lakes (albeit much smaller, one with flamingoes, the others you will see viscachas, as well as the very high altitude trees), all but one require short treks (about one hour to reach each one consecutively).
Thanks so much for you reply , Anybody else?
I have been to both places. My vote will go to Sajama park
I haven’t been to Sajama but did go to Copacabana a few years ago en route from Cusco to La Paz. Some photos and detail on our blog @ https:/… . Copacabana is reasonably touristy, but nowhere near as bad as Puno, the Uros islands etc. I found it a pleasant little town, a nice cathedral but the main reason for visiting would be the lake which of course, is unique. We took a half day trip to Isla Del Sol which was packed with tourists but the boat trip itself afforded some spectacular views of the lake and the Andes.
The drive between La Paz and Copa is also pretty spectacular and will involve your car going on one ferry whilst you go on another over a small part of the lake.