I don't think they are very competitive with anyone but yourself. I've helped out at the Dairyland Dare for the last couple of years. There are friends who sign up and compete against each other and there are people who just ride and stop at the rest stops and just have an enjoyable ride. I can't speak for the other 2, but the Dare has a wide variety of riders, last year there was a guy riding a Pugsley!
I did the Triple Crown 2 years ago, 100k on all three. Very challenging, great support, and even better scenery! The Dairyland Dare was by far the bigger of the three at that time. I know the 500 rider limit for the triple has been reached this year. It is not a "race" but timing chips are used. My opinion was Arcadia Brute was the hardest, Kickapoo Kicker had the best scenery and the Dare was the most popular since it has been around the longest. You can't go wrong on any of the rides!
I've done the triple crown and agree with dannwilliams. Hardest to easiest is Brute, Kicker then Dare and all are well organized with good parking, support and food.
The Brute is basically a series of 1 mile hills at about 7-8% (300-400ft climbs) that are about 5-7 miles apart with descents to match. In between you are generally in a flattish valley or ridge.
While the average climbing per mile is similar for the other 2 rides the pitches become less and frequency increases to the point where the Dare has as much rollers and false flats than distinct hills although there are still a couple bigger climbs.
As others have said, they are similar to a chip timed century type ride. Riders are released in waves every 15 minutes or so and faster riders tend to start earlier. There is an overall competition based on points for both distance and time, but you don't have to worry about hanging on to a peloton or look out for bunch sprints. It's pretty much just like a century on a hilly course.