If it is summer, then outside- you don't want your guests to be too hot. If it's winter, then inside- you don't want your guests to be cold or rained on. An alternative would be to host it at a venue that allows outside and inside. Somewhere with a big back door.
Well, it depends on the weather of the day you are going to have it. You don't want it to be too hot, too cold, or rainy. You want your guests to be comfortable. I personally would have it inside, but it's really up to you. Are you an indoor, or outdoor person?
its summer... outside