I like June better as it is a go outside in the evenings kind of month for me. I like the extra amount of daylight and warmer weather and less rain. Where as sunset is early enough in March that I don't get to see much sunlight when I leave work.

That said, the only challenge I did this year was the bus one which I did at a weekend, so the available sunlight didn't matter much. I think maybe I'm a bit bored of the challenges now though, to be honest.