This depends on your preferences. A green card will ultimately lead to full US citizenship in most cases but the status has both benefits and detriments. In addition to that, a green card is much more difficult to acquire than an E-2 visa. If you want to engage in a small business in the USA being a Grenadian citizen, obtaining an E-2 visa will suit your purposes. If you want to become a full citizen of the USA after a few years, then apply for a green card.