I'm going to say all of them and none of them.
Yes, DL was the one he constructed from start to "finish" although in Walt's own words it will never be complete. However, with DL, all of those hotels and diners popped up and didn't allow him to do all he'd have liked, hence the need for "the Florida project", so DL was a start, but obviously it was incomplete.
Walt dreamed of the FL project, with a DL type park - MK, and EPCOT. You can say MK is an updated DL, which learned from its lessons in planning. MK's utilidoors system is amazing and improves upon DL (in terms of that planning. I'm not going to compare WDW to DL in terms of rides, exerience, etc).
EPCOT is not what Walt planned exactly, but it has some of the spirit, and like all of Walt's Blue Sky ideas changed over time as times, finances, and the needs of the public dictated.
Even the newer parks that Walt never even saw a blueprint for (DHS, DAK, International parks), are part of Walt's vision not only because they have classic attractions and takeoffs on classic attractions but because they have Walt's spirit of innovation, or entertaining the entire family, etc etc.
I think it's all Walt's vision,
That having been said, I do want to go to DL and walk in Walt's footsteps, and I am fascinated by what his idea of EPCOT could have become.