My knowlege is limitted, but there are a few things I'm pretty sure of.

An LLC is generally much easier to form and incoporate than a 501(c)3* corporation. It might be easier to form a nonprofit at the state level, but I don't know what kind of protections that gives you and I don't what if any effect that has on your federal taxes.

Both will require you have some kind of corporate directors. Both will make it easier for you to get Directors and Officers Insurance. D&O insurance will protect the corporate entity year round in the event lawsuits, even if they aren't a result of something that happened at the event.

I believe the actual persons who serve as the director and officers are protected from personal risk by the 'corporate veil' whether you have D&O insurance or not. In other words, any lawsuits are against the corporation and its assets, not against the actual persons. They can't come after your personal assets if the corporation can not pay the settlement. That is probably conditional on the lawsuit being about over something official. If a director punches someone at the event and gets sued over it, obviously they would be personally responsible for damages because they were not acting in an official capacity. I'm sketchy on the details, so take what I say with at least a few grains of salt. This is second hand from various conversations I've had with PDF's lawyer-board member. I'm provided it as a jumping off point for more research, not gospel.

As far as I know, there is little to no difference between the liability protections afforded by an LLC and those conferred by a non-profit org.

I don't know how necessary it is you form a corporation right away. Your event insurance should protect you from most liability concerns, but if an individual organizer is named as a party in a law suit, I don't know how that works.

Personally, I think the only problems with operating as an LLC is that you pay more in taxes and some people may think it means you are out to profit. The drawbacks of being non-profit is you have to be very careful about who spends your money how. It doesn't seem to matter to the feds all that much if you are actually following your charter, as long as there is no hint of it being used as a tax shelter in anyway and isn't being used for the benefit of specific private persons that are somehow connected to the org.

For instance the PDF board was voting on a grant for a Burning Man Film festival. It was organized by local burners, but Larry Harvey was coming to speak and they were paying his travel and accomodations. Several of our board members are tied to burning man, either as part time employees or regional contacts. While it probably wouldn't have raised any flags at all, they all recused themselves from the vote for the grant just to be as on the level as possible. It is an extreme example, but the only actual one I have.

*There are many forms of non-profit besides chapter 3. That is just one of the more common. I think one burn is organized as a 'recreational club' (chapter 7 maybe?). You aren't required to have a board in that case, but I think you have to maintain a registered membership or some sort. Registered with the org, that is. I know very little about the ins and outs of incorporation though.