In my opinion (and three years working in the admission committee), it's less about the tone but the arguments and evidences you cite in the statement.
For tone, keep it overall professional and formal, do not use slang and do not write to them as if they're your high school friends. Write as if you're writing to a teacher you respect.
For your arguments and evidences, I'd suggest focusing on:
- A certain story and experience that gave you the epiphany, inspiration, or determination to pursue this study/career. Stay true to the experience and avoid using too many tacky expressions/cliches.
- Combination of training and past experience that have made you a unique and valuable member of the institute and field of study.
- Career aspiration with specific goals in mind. For instance, how would the degrees or positions enable you to achieve new goals. While the goals and aims can be of personal level, it's important that you can also integrate your own goals into a larger system (like the field of study, or the larger entities your field serves) as well.
The decision of whether to include some personality traits of one self is really situation-dependent. But if you want to let the committee know that you're a "good communicator," remember to provide concrete examples as well.
Hope this helps and good luck!
... the answers there kinda encourage to use informal tone. What do
To me, being "informal" can mean, among many things, use of slang, figures of speech, and conversation-like writing style. Some of these do add color to the personal statement but I'm reluctant to endorse the statement that one should go informally without clearly listing what kind of informal speeches are to be used. Even within figures of speech, some are more acceptable than others in a personal statement. "Deer in headlight" may be fine; "a kick in the balls" is probably not.
I'd suggest, as I have said, don't get bogged down by the tone. Be your polite and eager self, and make a case on the three points to persuade the committee members. Treat them like someone you respect and it should be fine.