From some basic research I've found that when romanizing じ and ジ we can use "ji" or "zi." Apparently "ji" is used by Hepburn romanization which is the most popular for non-Japanese speakers but "zi" is used by Nihon-shiki and Kunrei-shiki romanization. I read Kunrei-shiki is what is taught to Japanese elementary school students (and it is what my 20 year old Japanese textbook used).
Also, when doing a google.co.jp search for words romanized with "zi," google will sometimes actually ask if you meant to search on the Japanese version of the romanized word, so it recognizes it as Japanese.... but it doesn't recognize words when using ji.
So I figured "zi" was more common and better for Japanese people... but a Japanese person I know just old me "we never use zi and always use ji." So, what is the deal here... is one better than the other (and by that I mean is one going to be easier to understand or more natural for native Japanese speakers)?
As an aside that may provide context for an answer: the reason I'm asking is I'm trying to choose a social media handle with Japanese in it and am trying to decide on zi or ji...