How to reduce spectral leakage? We are looking at FMCW radar ADC signals and converting from the time domain to the frequency domain in order build a range doppler map but want to have the best signal to noise ratio possible.  

In order to reduce spectral leakage, we are using the Hann function.  It just seems to be accepted that we use the Hann function.

Are there any other functions that we should be considering?
If you want to have the best SNR possible, you put a null on the signal that is leaking it's energy.  In order to do that, you either have to know the location of the interferer or use an adaptive filtering scheme.  

If you want to stick with a fixed window, the Taylor window isn't a bad choice,  It's like a Chebyshev and rolls off further out.

A. Villeneuve, "Taylor patterns for discrete arrays," in IEEE Transactions on Antennas and Propagation, vol. 32, no. 10, pp. 1089-1093, October 1984.