Two very different breeds, in size, temperament, exercise needs and grooming requirements. I would suggest that you contact both Breed Clubs and ask for the names of breeders that you can visit and whether they have any breed days organised so that you can meet lots of representatives of both breeds. No matter what breed you decide on please make sure you buy from a reputable breeder that carries out all the relevant breed health tests - a once over by a vet is not good enough. Dobermanns should be hip scored by KC/BVA with a score lower than 10 before breeding. They should also be DNA tested for von Willebrands Disease as well as Eye tested. Leonbergers should be Hip Scored (with a result below 12), elbow scored and eye tested prior to breeding. Also make sure that you only buy from a breeder who follows the Code of Ethics of the relevant Breed Club, eg, does not breed from a bitch under 1 year of age or over 8 years of age, breeds a litter only to improve the breed, not just for financial gain. Check out this Dobermann breeders website, lots of good info on the breed and health issues kerioak.dobermann.me.uk/ .