Bin Laden apparently believes that directly attacking the US (the Cole, WTC, US-personnel in Iraq, etc.) is the way to "win the hearts and minds" of Moslems. A successful attack "proves" America is actually quite weak, despite all its technology and resources. Moslems in general, and Arabs in particular, see themselves as having been victimized by the West for generations now. Directly attacking the US, the ultimate representative of Western secularism and power, not only demonstrates that the West - and the US in particular - lack's divine protection, but also raises the self-esteem of all Arabs, and ultimately all Moslems. This is particularly so if a spectacularly successful attack was a "martyrdom" mission, since it also demonstrates the dedication of the true Sons of the Prophet. In this way, the jihad will gain widespread support, and drive the West out of the Moslem World ("Dar-al-Islam").
The apparent feud between Osmaa Bin Laden and Iraq terror boss al Zarqawi seems to boil down to what approach is likely to attract more followers quickly.
In contrast, it looks like Al Zarqawi believes that direct attacks on the US aren't all that profitable, given the vast resources (and excellent defensive capabilities) of the Americans. Instead, he believes the fastest way to win mass support is to attack the "tools" of the US, the Moslem leaders who are allied with America. Discrediting them will hasten their overthrow, and Islamist regimes can take power. This, he believes, is a swifter way to bring about the expulsion of the West from Moslem lands.
Despite these differences, of course, both men, agree that the ultimate goal of expelling the West from Dar-al-Islam is to lay a foundation for a "final solution" to the "Infidel Problem."
Bin Laden probably has the better "vision". Many Moslems seem to be uneasy about violence against their co-religionists, even if the latter are "misguided", particularly since attacks against Moslems are likely to result in the "collateral" death of innocent bystanders, including women and children. In addition, Al Zarqawi's attacks are often directed against what are viewed by many as "inappropriate" targets, such as mosques, funerals, weddings, and clerics who disagree with al Qaeda's vision of the future.