both are formal. 您贵姓？ning gui xing? 怎么称呼您？zen me cheng hu ning? less formal:你叫什么名字？ni jiao shen me ming zi?

Both are ok and very polite way in formal to ask others' name. In a informal situation, you can say 'ni jiao shenme mingzi?' or 'ni de mingzi jiao shenme?'. There are still a lot of way to ask somebody's name, and some of them are impolite, like 'ni shi shui?' or 'ni shui ya?', but it also depends on the way you how to say it and the person you are talking to, so you should be very careful of your tongue. Hope you enjoy Chinese. ^_^

formal way is like what you said:您贵姓？（but it only asks about family name) so if you want to ask the name,you can say请问您叫什么名字？（qing wen nin jiao shen me ming zi) and informal way is much easier,you can say你叫什么名字？（ni jiao shen me ming zi)