Hmn. I used to think the best way to watch would have been 4-5-1-2-3-6. Now that I think about it, 1 and 2 are sort of unnecessary, but still kinda needed, so the plot works out a bit better. So I'd say, the best way would be 4, 5, then a 30 minute version of 1 and 2, then episode 3, then 6.