drtor brings up a good point, but I would disagree with his conclusion. It is true that focusing on one airline FFP is not going to help much unless you actually reach an elite level and the advantages of that elite status are actually useful to you. I estimated your travel at greater than 25K per year, which would qualify you initial elite status on many programs. Furthermore, the advantages of that status seem very useful to me, and I would think to the overwhelming majority of travellers. While chance of a seat upgrade might be low, you will get one eventually. Add in priority boarding, waived baggage fees, etc, and this is a worthwhile benefit. With some promotions, like AA's DEQM event that most of us are anxiously hoping they implement again for part of 2010, you could qualify elite even faster. Even without that program, some FFPs have "challenges" that might put you at elite earlier. So when would it NOT be worth it to aim for loyalty to an FFP?
1. You will be flying less than the minimum necessary for elite status
AND
2. There is a significant difference in price between the proposed FFP and a competitor
AND
3. There is no accelerated method to gain elite status.
Otherwise, you should do it. Start with this:
1. Decide on the acceptability of Newark for some of your trips
2. Decide on the acceptabiity of MIA for your South Florida trips
3. Determine if you will be making a trip to South America again this year or next
4. Narrow down where you might be going in Europe.
With all that, examine airline and alliance availability to your destinations.
If the answer to #1 (Newark) and #2 (MIA) is NO, then Delta might be the right choice.
If #1 is Yes but #2 is still No, then Continental might be the better option (their FFP program is much better respected here at FT, it seems).
If the answer to both #1 and #2 is Yes, then that would bring American into the equation, and if 3# is also yes, then that would move American up even further in the rankings.
So, I think its worth it, but I can't help you any further with the actual program selection.