Trip to Amalfi Coast or Florence between March 9 to March 14

The Amalfi coast will not be green yet, the water will still be rather cold, and rain is more likely than later in the year.

If you only have 4 days (is it 4 nights or 5?), content yourself with Florence. You can day trip to Siena and Lucca if Florence does not hold enough of interest, but spending only a night-or-two in each of two places is a waste of precious time lost in moving hotels.

With your time limit, just ONE place.

I'd stick with Florence just because it's a long trip to the Amalfi Coast involving transfers. Since you don't give any particulars of where you are coming from or going to, the advice you get may not be the best.