I use 1/0 up to 4. I have switched from classic streamer hooks to mustad 3366. A 1/0 mustad 3366 is about the same length as a size 4 standard streamer hook. So you can tie the same size fly with a much larger hook gap. This will improve your hook up rate and appears to reduce the number of deeply hooked fish. I now tend to use either a 1/0 or size 2 mustad 3366 for most of my smallie flies.