We did the KTTK back in 2002 and we just did the Segway Tour in January. I say, DO THEM BOTH!!!
This is a tough decision. Yes, you do have to use a full day's park pass to do a tour. That said, here's what we did. For the KTTK Tour, we did the 8:30 AM tour and then remained in the MK after we were done. Our tour guide, Robin, was excellent. She explained the layout of the park, the architecture, some park trivia and more. We went in the backdoor at HM, JC, PotC and spent some time behind the scenes (SM and some warehouses) and in the Utilidors. Lunch was at Harbour House and consisted of sandwiches, chips, etc. We received a nice pin at the conclusion of the tour. It lasted around 3 hours or so. Other than lunch and being seated on a ride, there was no time for sitting. We had around 15 or so people in our tour group. We really enjoyed this tour.
We did the Segway Tour on January 26th of this year and really enjoyed this tour also. We did the 8:30 AM tour. Much to our dismay, the bus from POR to EPCOT did not start running until 8:00 so we got there just in time to get to Guest Relations at EPCOT by 8:30. We were supposed to be there by 8:15. Once we found GR (near the Electric Umbrella), we signed a waiver and headed over to Innoventions. The first hour is spend learning a little about the Human Transporter and then learning how to "drive" it. After a short restroom break, you head out into the WS for the 2nd hour. This is excellent, especially if you're a gadget/technology freak, which you are (me, too). This is an incredible device and you have to try it to believe it. You travel in single file for the most part with a tour guide throwing in some info about the WS countries along the way. There isn't nearly as much info given about the WS as there is info about the MK during the KTTK Tour, but who cares? That's not why I took this tour. There is a 15 minute period where you get to cruise around on your own, but you must stay within certain boundaries and not break the rules. Bring your camera because this is when your guides will take photos. Unlike the KTTK Tour, I would consider doing this tour again just because the HT is so amazing! You get a nice pin at the end of this one, also. This tour has a maximum of 10 people.
This is a tough choice. Have fun choosing!