I totally agree with those who have said that there should be a mixture of the two -- startles and scares. I try to have both in my haunt, as well as a place or two to laugh. This year, we are going to try and incorporate scenes that are just there for eye candy, too. Such as the "Half It" room were everything is halved. (Half a chair, half a coat rack, half a trash can, etc.) It was inspired by Willy Wonka and the Chocolate Factory.
Startles can come from anywhere and takes but a second -- the creature is there and then gone like a flash. A startle usually results in a scream with a person's feet still planted as the threat is no longer a, well, threat.
A scare takes longer and is a process --a process of building up emotions and working on their fears. When combined with a startle the results are usually the feet taking the customer away from the scene.
I've found that it takes more $$ to create a good scare than a startle (Black mazes not included
). Scenary, lighting, sound effects, music and detail, detail, detail ALL take a part in a good scare.
I try to never repeat a startle more than twice. It becomes old hat after that and predictable. BUT, variations on a particular startle work well. For example, drop panels are GREAT and are almost always a guaranteed startle if it is disguised correctly. I have two drop panels ( one regular that goes straight down with a bang and one that goes out from the wall on chains). But, I also have a cabinet door that the actor pulls in towards himself and leans forward through the opening for a startle and a HUGE white trunk mounted on the wall with the words "First + Aid" written on it that the actor pushes the lid open on and bangs against the table in front of it for a good startle.
Animatronics/Pneumatics can be used for a startle and can set things up nicely in a scary scene, too. We are using them for both. Air cannons are great startle equipment and Coffin Risers can be used for both (depending on PSI). I could go on and on...but, I won't. LOL!
Have fun making them scream and run!! You're only limited by your Scare-magination!