Be NICE, but be WISE.
Being nice is better if you are wise enough to know why, when, where, and how to be best in that personal quality. Yes, being nice is a great personality trait. However, it will be even greater if you are aware of your space and impact when you exhibit this personal quality.
If you are a genuinely nice and pleasant person, the chances of you being taken for granted, manipulated, overseen, ignored, and (over) used are high.
If you are unwise with your niceness, your niceness will be seen as your weakness, not a strength.