Hi Lisa,
First of all, just so you know, I have several hundred hours driving an airboat IN the true Everglades -- Everglades National Park (but I don't do tours).
Airboats are very versatile boats and can be driven either in very shallow marshes (like Everglades) or in rivers and lakes. The design of the airboat will vary a bit, but the key is the venue.
Riding on an airboat on a river or lake is just like riding any other boat on the same waterway, but louder. Much louder.
Riding an airboat in a shallow marsh is a much different, much better experience.
Do NOT expect to see much wildlife on an airboat ride. Yes, you'll see some wildlife, but in the tourist context, it is most like a carnival ride -- fun, something you do once and will always remember (like a hot-air balloon ride), but not a way to enjoy nature.
*****
When you say "near Kissimmee," that makes me think the airboat tour is somewhere on the Kissimmee River which runs roughly from WDW south to Lake Okeechobee.
That's going to be a river ride. It might be enjoyable, but it will be nothing like the true Everglades. They'll claim it is, but it's not. No matter what they say, there is no Everglades north of Lake Okeechobee.
The historic Everglades extended from Lake Okeechobee south across the Florida peninsula to the oceans (Atlantic, Gulf of Mexico, and Florida Bay, which is the body of water between the Florida Keys and the mainland). Today, that landscape is radically changed but much of it still resembles the original Everglades.
To the east of Lake Okeechobee (between Lake O and West Palm Beach) is the Loxahatchee National Wildlife Refuge, managed ty the US Fish & Wildlife Service.
To the south of Lake Okeechobee, first you have a very large area of agricultural lands, and then more of the Everglades.
Once you get past the ag lands, you'll have the same general type of landscape you have in Loxahatchee -- similar to the original Everglades -- vast sawgrass prairies dotted with tree islands. I would notice the difference, but you will not. Either the Loxahatchee area or further south would offer you a fairly realistic Everglades experience.
Somewhat further south (west of Miami-Ft Lauderdale), you have more realistic Everglades airboating. This is the area where you'll get the best Everglades airboat experience, but it's 4 hours or more from WDW.
Hope this helps. Let me know if you have any specifuc questions. I probably can't comment on individual airboat companies (for a variety of reasons, including I haven't take their rides), but I'll try to help as much as I can.
