I think the African clawed frog is a good first frog, providing they are legal in your area. They have been used in genetic and molecular research since the 1940's. Xenopus laevis are fully aquatic and easy to care for. I understand that there was a significant population of clawed frogs in southern Wales during the 1980's/1990's. I understand by now these feral populations have declined or become extinct. The University of Portsmouth European Xenopus Resource Centre | European Xenopus Resource Centre | University of Portsmouth has some research information. Here is some good care information RSPCA || Xenopus.