You'll often find that people will say names have energy and that different names will have different energies. As stated above, you can go by whatever name you prefer, but you can also choose a name that represents you. Not everyone works with a magical name.
We also tend to find that instances involving preference for different names are more spiritual or religious in nature than magical. If it comes to that, just ask the spirits or deities you are involved with which name(s) they prefer.
what is the spell in question? writing your full name is used to specify the spell but if you have a nickname you could go with that, or write your full name like 'Jane "LaSirene" Doe'. if you have a magick name you use in circle, that one would be the most personal. the reason you write a full name is to personalize it, so use what you feel is best. same is true for using someone elses name. if you just know their full name, write it while visualizing them, or you could write their nickname like the above example. the point is to personalize.