1) A boy who wears GAP-like casual clothes (chakis, casual shirt/sweater, sneakers, etc.).
2) A boy who wears double-pleated and cuffed dress pants, black dress shoes, dress shirts with a tie, and carries a briefcase for his schoolbooks.
3) Any variation of 2 you might want to consider, such as removing the cuffs and double-pleats.
Note that I'm talking about clothes the boy wears every day, not just on special occasions. And again, I'm talking about university students of age about 25.
In general what types do young women like that prefer? It seems that 1) are most common for boys these days but that doesn't mean we know what women think.