Taking into account that you'll probably want most people able to enjoy the image, I would go for #2, simply because it'll look better on monitors that arent quite that bright.
However, artistically, i like the contrast of #1 better...

I think Bryster s right when he says both are too dark. You can still capture the same mood if not a stronger one, by boosting contrast and brightness both.

Maybe you could try taking the 1st version, and try to boost the brightness and the contrast both so the brightest area's become brighter, but the darkest areas remain as dark as they are in #1
If you have photoshop, try using the auto contrast, auto color, auto tone (if you have cs4) and auto levels.
Personally i like to duplicate my original image to a few identical layers, and apply these automatic filters each to their copy of the original image (each in its own layer). Then you can properly see what they do to your render and combine features u like.

Also, after you have your brightness and main color tones set out, you could apply a "curves" adjustment layer to do some final tweaking.
You can also use layer blending modes on adjustment layers so by putting it to "color" blending mode you could play around with the colors without adjusting the overal brightness and contrast of the image.
This might come in handy because big changes in brightness and contrast tend to also change the perception of color and saturation in an image.

If i may add my peronal artistic vision; i would try making the bright area's of the image nice and strong, while leaving the shadows dark, but onyl entirely black in the darkest regions like the top right corner so you dont lose definition in the nebula's on the background.
Then i would make the yellow highlights slightly more orange and add a subtle more deep blue-ish tint in the dark area's. Then perhaps even, if you feel up to it, the slightest hint of green in the lower end of the midtones, or higher end of the shadows so the dark areas would flow from a deep blue just a little towards a really dark aqua before hitting orange and yellow tints in the bright areas. It'd probably fit the sort of oldschool sci-fi feel really well.

I could upload an example but i dont wanna go runnin wild with your challenge entry...

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