Currently the Altea Aerospace XR2-Ravenstar and the (coming) S3 Hyperdart.
The XR2 seems the most "real" in the sense of it actually being (looking like) a plane. And it's so detailed in terms of system modeling in addition to that killer look, that it's just hard to ignore.
The Hyperdart also looks absolutely killer, and has the allure of (promised) realistic modeling, as well as one of the BEST Virtual Cockpits I've seen yet (basically everything doable, is doable with a switch, lever or button).
If I could take the missing part of each of those 2 and mesh them (the VC in the XR2 and systems modeling in the HD), I might forget to eat. lol
I also like the concept of the Dragonfly and the Shuttle A for their "realistic"/"possible" natures.
And I'm watching SSU with much anticipation while I brush up on other skills before taking on even what's already done. That will definitely take a place on that altar as well.
LOTS of other really cool concepts and models, but the lack of a VC or systems modeling (and especially if it doesn't even have so much as a panel view) REALLY puts me off (kills immersion for me), which is a shame because many of them are definitely high quality everywhere else.