A Jitsu-in, which is the most official type of seal and is registered with the city office, needs to match your legal name. So mine is just my family name in latin characters. It looks funny but does the job.
For less formal seals you can pretty much pick whatever you want. For those I use my family name transliterated into katakana.
For less formal seals you can pretty much pick whatever you want. For those I use my family name transliterated into katakana.