A Poll to stimulate your mind. *DELETED*

[PvK]

They're all best. No seriously, I like them all. I thought maybe the upper-left was a front view of the upper-right one for a second.

[Baron Munchausen]

From the 'two dimensional' point of view, i.e. from the SE combat perspective, the upper right looks coolest. It will be easily recognizable from the angled view or from the top down view. It also has the most 'surface' in the single plane where ships and units will be moving, so offering the most space for firing points. The others will be harder to recognize from the 'top down' angle and also have fewer firing points.

[Kamog]

I like the lower left one because of the unusual alien-looking appearance.

[ToddT]

for pure aesthetics, the upper right, though the lower left has its appeal, maybe some altering of textures to reduce the mismatch in the primary structural elements.
the lower right reminds me of an episode an episode or two of STNG. the upper left not sure.....

[Xrati]

Upper right, but nice work on all of them really!