I'll go through each entry and comment on it now, since they are finally done, and try to find my favorite. It's kind of hard because tracks have very varying qualities to them, so I can't really decide which one I like the most.
Now off to re-listening
Desert Machine - by AditTechno
This entry embodies the laid-back "cool" side of steampunk. It's easy to bob your head to, and it has a lot of mechanical sounding noises to simulate steampunk elements, and they are all done through instrumentation and not simply sampling. It has a good flow to it, the consistent rhythmic backing and modulations that make sense, and a melody that doesn't try to sound too imposing or all important, the production is tight, it has that midrange-heavy synthy sound that's really catchy.
Siege on Compoundville - by obie
A very atmospheric piece that transitions into metal. I have a feeling it cuts off somewhat unexpectedly and feels unfinished. Some synths used during the metal part in particular don't feel like they belong to the same mix, the production of the metal part feels way too dry to my taste, so more care could've been taken during production imo. Not a huge fan of sampled steampunk noises. Still, I really love how it transitions into a much heavier piece, and even though I love metal, I like the first part more, tho I love the composition overall. Despite the flaws, I still like it.
Clockwork Madness - by Brambleclaw
This one has been my favorite since I've heard it completed. I don't like how the orchestral synth seems to cut off since it is either not midi'd well enough or the library is cheap. Also could've done without the random, deep, steampunk noises, since I don't feel like they do anything musically. The high pitched well integrated steampunk noises, however, are great. At some point the orchestral composition loses a bit of the direction, but it comes back to the beginning riff which is my favorite part of the composition. I can see steampunkish flying ships cover the sky to join the battle as I listen to this.
Sphere of the Architect - by deepstrasz
An extremely atmospheric piece, that seems to give up on trying to sound like tonal music in the beginning and instead strives to directly transfer the feeling of "steampunk" through an arrangement of noises. As stand alone music, unfortunately, it doesn't do much, which isn't something I am to thrilled about, but I can see compositions like this being really good background to some sort of a (non steampunk specific) setting. It picks up the pace later, though I feel like it's kind of too late in a way, since it lasts for more than 7 minutes. It's a shame that more of this composition wasn't like the last few parts of it. It evokes the feeling of a dystopian steampunk world with a glimmer of hope, so I'd say that thematically, this entry shines.
The Grand Tour - by Donut78
This doesn't sound decidedly steampunkish at any rate, but it does sound like very proper adventure music the likes of which you can hear in movies and games. It's very upbeat, epic and well arranged. Aside from not sounding like it has much to do with the theme, I really have no complains for this, it's just, as I said, very proper adventure music. It is kind of short, but it certainly gets its point across.
Locomaction - by GhostOfPast
This entry is just a ton of fun. The vibe you've gone for is very well executed, and especially the combination of 8/16bit elements with more refined tracks/instruments. I can see it sounding as a train, and I can already imagine a 2D game where you're chasing a moving train and this goes in the background, so you get lots of points for that. The production is clean and fitting for the style of music that it belongs to. I love how each part of the composition transitions into another. As I said, it just sounds very fun, and I like a lot of soundtracks that sound like this, you could have this on repeat forever and not get bored (which is what game music has to be, too).
Conclusion
I don't think I've ever voted in a contest where it's basically anyone's game since so many entries are of such high quality, even if the qualities in question are specific to the entry, so I'll think for a while and decide which (thankfully, two) entries I am going to vote for.