If you have an opportunity to do both, that's great! It gives you more chances for profit. However, if you must choose one or the other I would say an indoor event is your better choice.
You can get much more creative with your scenes because they don't need to be weather proof. You won't need security at night to make sure nobody gets in to steal or vandalize your attraction. And the biggest thing is you won't have to rely on perfect weather every night.
If you are only outdoors you will not be very busy when it's raining or even snowing. That has killed a lot of attractions over the years. I would not want to have that to worry about every night.
I am sure others will disagree and have a bunch of reasons why outdoor is better. This is just my opinion!
1986-1997 (Mutilation Mansion,) 1998 (Screamers Haunted House,) 1999 (Evil Intention Haunted House,) 2000-2001 Concept Creator/Business Partner (Urban Legends Haunted House,) 2002 Floor Plan Designer and Consultant for a (Haunted Barn) Owners had city challenges & were never able to open, 2002 Floor Plan Designer/Construction (Fright Nights Haunted House) 2003-2012 Now retired Owner (Deadly Intentions Haunted Attraction)