Crossing the Gulf Stream from Miami to Bimini, or from Ft. Lauderdale to West End, is a choice all Bahamas cruisers must make. Their decision is usually based on what parts of the Bahamas they plan to visit. (By the way, crossing the Gulf Stream marks a milestone in most cruisers' lives. For many of us, it is our first experience making an offshore, overnight passage.)
For example, if their goal is to visit the Exumas and the southern Bahamas, then the Miami-Bimini-Chub Cay-Nassau route is the most common one to take. If the weather's good, expect your GS crossing to take around 12 hours to Bimini (60 miles @5 knts.). From there you've got almost 70 miles across the Banks to Chub and another 40, or so, to Nassau. Some cruisers will opt to anchor out on the Banks overnight, while others will push on through to Nassau.
This route is probably the most popular one taken during the Fall/Winter months as cruisers are seeking to reach the warmer weather found in the Exumas as quickly as possible.
If visiting the northern Bahamas is your goal, then head over to Grand Bahama (West End). From Ft. L., crossing time should should take around 10 hours. From there it's about 40 miles to the anchorage off Great Sale Cay. From there it's another 30 miles to Spanish Cay, or 45 to Green Turtle Cay. You can clear customs at both locations.
The Sea of Abaco is a very sheltered and scenic cruising area. This route is a popular one for cruisers wishing to see the Bahamas from north to south. It is also popular in the Spring as many of the folks who wintered in the Exumas come north to the Abacos on their way home to the States or Canada.
One final thought.
When planning a trip to the Bahamas you cannot overlook the effect that weather will have on cruising schedules, especially during the winter and early spring. Be prepared to wait for weather windows and factor this into your cruising schedule. Waiting a week, or longer, for the right weather is not at all unusual.
Keep planning and refining your trip. Don't hesitate to pickup some cruising guides and chart kits.