Here's how the biggest titanosaurs rank out in first-last place:
1. Tie between Alamosaurus (referred Mexican fibula + Fowler & Sullivan's neck centrum) and Puertasaurus (1 cervical, 1 dorsal, 2 unpublished caudals). Both of these animals were around 120+ ft. long and probably 100 tons.
2. Tie between Argentinosaurus and the "Chubut Monster". Both of these animals were probably pushing 110+ ft. long and 80-90 tons
3. Tie between Ruyangosaurus (cervical rib, anterior and posterior dorsals, additional unpublished dorsals, dorsal rib, upper femur, tibia), Notocolossus (dorsal and caudal vertebrae, foot, and limb elements) and "Argyrosaurus" (referred femur FMNH 13018) - probably between 75-90 tons. Ruyangosaurus may have gotten longer than 100 ft., Notocolossus and "Argyrosaurus" were probably not as long but still huge at 90+ ft.
4. Tie between Dreadnoughtus (majority of skeleton) and Par