To be selfish means to consider oneself above the well-being of others, or holding one's self interest as the standard for decision making while supportiveness in the context of this content means to put the interest of others first.
A lot has changed over the years, so are humans. People no longer think and act like the people of the old where empathy and being supportive was the order of the day. Selfishness nowadays has become a tool for smartness and survival. Greed has set in where nothing we have is ever enough thus feeding the belly of selfish thinking.
Selfishness is a trap, its birth by the feeling of "me" and once the voice of the "me" is louder than the "we" our self-interest begins to play in everything we do. With the recent hardship, people are most likely to think of themselves first not minding others and once we have enough piled up for ourselves, we see that as being smart. One character I noticed from my grandma when growing up was that she worried about the well-being of others more than herself . She always believed people needed her help and she was always available to render help even though not every one of them appreciated her kindness.
Which is more beneficial?
There's this saying "if you want to go fast, go alone, but if you want to go far, go together". This clearly speaks in the area of selfishness and supportiveness. One who is selfish may have that luxury of gathering for himself but it's often for a short time and most times, it comes with bitterness, sadness and at the end a consequence. But true happiness lies in being supportive. There's this joy that comes with the knowledge that you're the reason behind someone's smile. One who is supportive always has the love of the people around him and his act might be his saving grace someday. Even though selfishness looks like wisdom, it's a trap to destruction but true happiness comes from considering the interest of others.