Spin coating/casting is highly repeatable and produces pretty uniform films over large areas. I am not sure what you mean by the "drop method" but if it what I know as drop casting (you place a droplet on your substrate and wait for the solvent to evaporate), it is neither repeatable nor produces uniform films, it limits you to small samples and it takes a lot longer. 

Where possible, I would use spin casting

Rob

If it is a crystallization of the polymer melt, and even more the crystallization by solvent evaporation, with the drop method it is really hard to get uniform thickness layer. In the latter case it is essentially impossible due to the rather complex nonequilibrium physical processes that occur in this case (the transfer material to the periphery of the drop, the occurrence of temperature and concentration gradients etc). The control of these processes is very complicated. As a result, the thickness of the boundary layer on the drops can significantly exceed the thickness layer in the center of the drop. Spin coating gives much more uniform thickness. But in this case it is necessary to take into account local inhomogeneity of the substrate surface, which will result in a nonuniformity thickness of the deposited layer.

I agree with Robert. I would only add that with spin-coating you can also control the film thickness (changing either concentration of your solution, spin speed or both will affect the thickness of your film). 

Thanks to all for valuable information. 

spin coating is the best method to control thickness and uniformity of film. on glass and ITO coated glass too

Robert Temperton I was looking for an answer on how to perform drop coating when I came across this thread. I need to form a mask for a nanosphere lithography process and the paper just mentions "To form the deposition mask, approximately 2-3 microL of the nanosphere solution was drop coated onto the 18 mm substrates". Does this mean I just drop it onto the surface and then thermally evaporate it?

Arti Tyagi Did you happen to get an answer to your last question? I am looking for exactly the same thing, but in the paper I'm using they are drop coating antibodies on a PSMA membrane and I was wondering the same thing. Thank you

George Mihai Avram unfortunately, no. I ended up not doing that experiment. But I did talk to some colleagues of mine and they said that yes, that is what it means.

Arti Tyagi ok, thank you for your answer.

If you want to get a layer that is uniform in thickness and composition, then of course spin-coating.

Thank you Alexander Loskutov