Personally I think about any breed can be a good pet, you just want to find one that has been very handled and is friendly. I have or have had nubians, alpines, boers, pygmies, nigerians, one fainter, and one LaMancha.
I think the nigis have the most personality!
My LaMancha is the only one I've had, I got him pretty young (2-3 months), but he's never been overly friendly, he's very food motivated and as long as you have food or treats he's your best friend.
Most people looking for a pet want one of the smaller goats, nigis, pygmies, small fainters, all would be nice! Personally I like the colors of the nigis and fainters!
For a very long time I would have said if I could only have one goat as a pet it would be a nubian, I love nubians, always will! Always thought I'd prefer the biggies! I generally thought of the pygmies when I thought of minis, and although they are nice, they just aren't my breed. However, I have grown to love the nigis, and they are now ranked right up there w/ the nubians!