There is, of course, no way to quantify how effective a president is.  The US did very well during the Clinton administration, but does not necessarily prove anything given that the country, arguably, faced less daunting challenges during the 1990s than it has since then.  Overall, I would say that Clinton was very effective, but not as effective as he might have been if he had had a little less hubris.

In many ways, Clinton was very effective.  He was an excellent politician in that he had the capacity to appeal on a personal level to a fairly broad range of people.  This is not to say that everyone loved him, but he did do a better job of appealing to a broad range of people than most politicians do.  Perhaps as a result, Clinton managed to get some important things done.  He presided over welfare reform.  He produced balanced budgets.  He did this while working with a House of Representatives controlled by the Republicans. 

However, Clinton could probably have been more effective if he had been more disciplined.  His foray into the issue of gays in the military helped to derail his (arguably more important) efforts to implement health care reform.  His cavalier personal behavior and his apparent feeling that he could maneuver his way out of trouble with carefully chosen but less than straightforward words led to his impeachment.  This made it very difficult for him to accomplish much as he was engulfed in scandals.

Overall, then, Clinton was quite effective, but perhaps not nearly as effective as a man of his talents could have been.