Just remember size does not equal meat. You can have a big goat like a Saanen but they do not have a lot of meat because they are dairy. On the other hand, a big boer will have meat because it's a meat breed and bred to have lots of muscling.
Thank you all for the response , I agree that the boar is the ideal meat goat how ever the saanen breed I saw at lancanster is definitely bigger than my Nigerian dwarf, I hope to have extra meat and some height if I cross them. I intend to have them in ratio 3 to 1 i.e. Boer ; Saanen (to cross my Nigerian dwarf)