Florencce

if you have to see David then acedemia, the uffici has more other things to see. you should get ticket in advance - the line will be long at both places in May.

The Uffizi has it all over the Accademia--it has the greatest masterpieces in all Italy. The collection is not that large, though, and your visit should take one to two hours. It's possible you do have time for the Accademia as well, since it's only a few blocks away.
Yes, you need reservations for both, at least a month in advance. If you're staying in Florence, your hotel should be able to get them for you. Otherwise get them online.

See both. It should not take you very long. In my opinion, at the Uffizi, the most interesting and important works are those by Botticelli. At l'Accademia, the most important work is the David. There is no reason for you to choose, you can have your cake and eat it too.

If your time is that limited, the Uffizi is a priority. You can see the copy of David in the Piazza della Signoria which, though it is a copy, is where Michelangelo intended the statue to be. If you plan and reserve in advance, it doesn't take much time to see the real thing in the Accademia.

Thank you akk so much for your help.

For painting, the Uffizi. For sculpture, the Bargetto (much better than the Academia, whose claim to fame are the Michelangelos). The Uffizi is almost always crowded, and because it is small, there can be lines to get in, even with advance booking. I don't think the Bargetto is ever crowded. They are all within a few minutes' walk of each other. The Academia can been enjoyed in a hour, the Bargetto in 2 hours or less, the Uffizi in not much more than 2 hours. For the Uffizi and the Academia, you will waste too much precious time standing in line if you haven't booked in advance.