They're both cool, but it seems like the word MAME is just out of place on the Galaga marquee. What extra value does the word MAME add? Nothing in this case. The MAME X marquee feels a little more personalized, and the name makes more sense in that connotation. In the Galaga MAME marquee, why not just make it "GALAGA" drop the mame. No one (outside of the various MAME forums) EVER says to me "Wow, MAME that is such a great program" They just say "WOW, I loved Galaga, (or defender, pacman, etc)
<rant >
I wish MAME could have a different name. I mean, I love the program and all, but it doesn't have a very good arcade *ring* to it. It would be great if it was supercade, or ultracade, or arcadeforall or some other silly name that otherwise I'd be too embarrased to use on my cabinet without a good reason. An arcade machine is such a showpiece, it has so much cultural baggage, you know? When you see a machine you remember the memories come flooding back. The word MAME on a machine to the uninitiated just makes it seem like you have a bad arcade game they never heard of (until they see it in action, of course.) No slight against all the MAME cabinets out there, but the word mame itself doesn't really add any personality, legitimacy, or added interest to the average arcade cabinet.
</rant>
It's so hard to come up with a good marquee that has a real nostalgic feel without just throwing a bunch of screenshots, marquees, or characters all over it. Throwing the word "MAME" on a marquee doesn't do it for me.
Anyway, this is just one man's opinion, but I wouldn't be too broke up by making it simply a galaga marquee if I were you.