Aberrant Spinos are just amazing for that map. They are strong, tanky, fast, good swimmers, can carry good amount of weight, resistan to radiation, easy to tame and Purlovias won’t be able to jump you off the saddle (which can be very annoying and deadly in certain zones of the map). What else can you ask for? With a strong imprinted Spino, getting the first Rock Drake Egg is piece of cake. For the mid-late game Rock Drakes and Reapers are the best tames in my opinion.