Hi there! I don’t know much about making an outdoor ticketed event but I do know quite a bit about hosting events! I have hosted events for my and other startups. My advice to you is to double check what exactly you need because investors and sponsors are two completely different things.

Investors

Investors are perfect if all you're looking for is some more money. They will probably ask for some percentage of the profits or something similar to that. They can help open more doors via their connections but they aren’t forced to do so. Plus some of them might have experience in this type of event and they could be willing to help you out. However, like before it is up to them if they want to. So if all you are really looking for is more money, then investors are the right choice for you.

Sponsors

Sponsors tend to be more active in helping set up the whole event. Plus, different sponsors bring different things to the table. Not only can they supply food and drinks for the actual event (you probably get a percentage of their sales) but many are probably experienced in the event you will be running. Meaning that they can bring their experiences and open other doors for you. Another upside is that some sponsors might also bring in money plus food or drinks.

In the end, the choice is yours. If you are only looking for money, I would suggest going for investors. If you are looking for more, perhaps have someone supply food or drinks, then a sponsor is your choice!