I must agree with several of the replies to this. For one, you can't use a dog as just a sex toy. When you get a dog, it becomes part of your family and should be treated as such.

Another thing is German Shepards and Labs. Out of my own personal experiance, they seem to be the best for starters of zoo. That's just my personal opinion. I'm sure other people have others. Both have decent sized member and are VERY smart for educational reason.

Again. Please realise that you have to treat the pet well. Good food, shelter, much love and affection. That love and affection comes WAAAAY before sex.