Each weekend has something special about it. Of the ones I've done:
Disneyland Half - it's the opening race weekend of the RunDisney season, and the themes for the 5/10/Half change every year, so there's always something new to surprise you with! Plus, you run through Angels Stadium which is packed with thousands of Boy and Girl Scouts cheering for you. It's incredible.
Wine & Dine Half - during my favorite time of the year at Disney: Food & Wine Festival. That said, the real unique part of this race no longer is a factor (night race), but it was pretty cool finishing the race in Epcot at midnight and getting to hang out in the park until 4 a.m., eating and drinking around the world and partying.
Princess Weekend - probably some of the best on-course entertainment of the races I've done. I loved that one of the first stops is all of the Princes, I liked the super-hot guys in tuxedos by the golf course, and of course the carriage and horsemen you can pose with once you get back to Epcot.
Tinker Bell Weekend - Pretty much perfect weather, a fast and flat course, and I really loved so many mom-daughter combos that participated, or seeing so many kids out on the route cheering on their moms during the race. And the Red Hat ladies in downtown Anaheim? Amazing. One even called me over and hugged me because she said it looked like I needed a hug - boy did I! And even though I won't do it again, the Neverland 5K is easily the most unique race RunDisney offers right now and should be a bucket list race for anyone that enjoys RD races. I hope they never change it logistically.