FWIW, I operate both a daytrading program and a long-term program (months to years) so I've got no bias for or against either. In fact, I believe that the optimal strategy is to trade both with risk equalized among them, as they tend to be noncorrelated. The trick is to define "risk" in a way that is consistent with one's goals since it is impossible to equalize something that is not defined properly.
Based on my analysis of my own work as well as the published returns of successful traders of both types (note that there are more published returns from long-term traders than daytraders by a wide margin), one should expect about the same risk-adjusted returns from daytrading as long-term trading.
Capacity is much, much higher for long-term traders, but the minimum starting capital for daytraders is much, much lower. Those seem to be the primary drivers of people to one or the other.
jj