Hi all Paul here from little ol' New Zealand.Spraying as said above is The best way patience is needed to get the masking perfect but as you can see you get a great result, I try to use Tamiya/Testors sprays as all the others are designed to be used on a full sized car so they really spray too much paint.Also if you fill a tupperware container with hot water(from the tap not the jug) and place your spray cans in it the heat thins the paint it comes out way nicer.
If I brush paint these on my 1/25th scale plastic kits(of which I have not touched for a while)I use a flat modelling brush form the model store,load a little paint and instead of using the tip which will fan out and get paint everywhere you don't want it use the side it holds it's shape and lays down a nice line. Alternitively you could use a fat/flat black marker pen.These tecniques do work work!! Honestly.Go the Masking tape!!!!