you will probably find it a lot easier to get a whippet than an otterhound. the otterhound is a very, very vunerable breed and not many litters are bred. infact if im right i think they are top of the list for lowest litters born each year. so you may find you could be on a waiting list for a long time, and most good breeders will prefer there pups to go to people with experience of such breeds, and as so few are bred and they have a huge waiting list they can be very picky. do be careful which ever you buy where you get your pup from. try the breed clubs. visit a few breed shows talk to breeders there, good ones will interogate you more than you them. research what health problems are in what ever breed you go for. if the breeder doesnt health test there breeding dogs and provide you with the health certs, walk away. if they are raised in a dingy shed withough proper socialisation, walk away. if you can ring them up and they have a pup waiting for you, be suspicous. and most definatly insist on seeing the mum with the pups, and if possible any other relatives espcially dad. whippets and definatly otterhounds are not breeds you would generally find bred by your average puppy farmer or back yard breeder but still if you are going to but a pup choose your breeder carefully. you might pay a cheap price to buy your pup and feel you have got a bargin but you wont have when you are at the vets all the time.
regarding the choice between the two breeds, if you have not had much dog experience i would go for a whippet. neither would be my choice of first time dogs but out of the 2 the whippet would be better. otterhounds are huge dogs and are basically a nose on legs. you will find them hard to train and walk. if you are into slogging about the countryside for hours on end following your huge nose on legs fine, if you dont mind a filthy house with hair everywhere fine. im not saying they arent lovely dogs, but you really need to speak to people who have the breed. try going on dog forums, one i go one is called dogpages and i know there are people on there who are owned by otterhounds and whippets. a whippet would make more of a pet and be happy with the gentle walks as long as theycan run and your house wont be taken over by a whippet like it will an otterhound. an otterhound well they are just something else, scent hounds are not the easiest breeds and as lovely as they are otters are very houndy.sorry to burst your bubble but i would definatly say out of the two go for the whippet. you probably wouldnt get an otterhound anyway and im pretty sure they go for a lot of money, well they would wouldnt they. hope that helps.