I used S04 for a bunch of batches in a row and eventually decided I didn't really like it. To me, it has a sort of tart/ "twang" thing going on that I don't really care for. Other people love it though so give it a try.
Windsor is excellent I think but you need to keep the fermentation temp. down (<=18C) or you'll get "fruit salad". Also, it attenuates poorly - my last beer attenuated less than 60%! My latest batch is currently fermenting with Windsor and Nottingham together. The idea is to get the nice English flavours of Windsor with the attenuation of Nottingham. I'll post back with the results if anyone cares.