Just a note here, I never play world maps. As such, my decisions are going to be based on the most 'interesting' and deserving civilizations, not the ones that would fit best on a world map.
Here are my opinions on all the Civilizations in this list. I'll mostly choose civilizations based on how unique they are, how well-known they are, how interesting their leader will be, and how fun they'll be to play for/against.
Abysinnia/Ethiopia Definitely. They had an impressive culture for such a poor region, and we need more African representation. I'd also choose Ethiopia over Abysinnia. All Abysinnia gave us was cats
Aborigine I'd say that Australia needs the representation, and the Aborigine are the only true choice. Some people claim that they never developed past the stone age, so shouldn't be counted. But the Aztecs, Iriquois, Babylonians, Romans, etcetera never developed into the Modern Age. Does that mean they shouldn't be included either?
Austrian I don't consider this a true civilization, just another European political division.
Dutch Although they are definitely a worthy civilization, we have *way* too many European civilizations in the game already. Dump 'em.
Hittites Errr... Who?
Hungarians Although slightly more deserving, I still think they fall under the same problem as the Austrians.
Inca As one of the most important civilizations in the Americas, I say they definitely deserve to be in. For their time and location, the architecture and road system they built was incredible
Israel/JudeaThe Israelites began religious roles, rites, traditions, and attitudes that infiltrated almost all of European civilization, and then most of the world. I'd say they definitely deserve a spot.
Macedon I am not voting for a civilization that sounds like a cookie. Besides, aren't they just a division of Greece, or am I mistaken?
Phoenicians Alright civilization, but there are too many similar civilizations already represented
Polish Yet another European civilization. I honestly don't see why they get so much support, since their empires have always been small, they've never been extraordinary in any respect, their culture seems to me to be a mini-Russia, and they keep getting trounced in modern times.
Polynesian They've built an impressive culture on some chunks of land in the middle of the world's largest ocean. Quite impressive ^_^
Portuguese It fits in with Spain, France, and England, but we have too many European civilizations with similar traits already. There just isn't enough differentiating them from other similar civilizations.
Siamese/Thai I don't know much about these peoples.
Sioux/Dakota Although I'm a fan of Native American rights, I don't think they need to be over-represented. Besides, I've never been a big fan of the Sioux. If you want a good Native American civilization, I'd choose the Anasazi.
The Anasazi built a massive culture in the middle of the South-West desert. They had those huge pueblos built into the sides of mesas, and had an extensive system to gather food in the area.
Slavs I am not choosing a civilization that gains a total of one sentence in my history book...
Tibetan Unique, well-known, interesting leader. That's what I'm looking for in a random map game, so I say let 'em in 
Other The only other civilizations I suggest are the Anasazi and the Australians. I say the Anasazi because the American Southwest could use filling out for all you RW players, and I believe they were the most advanced of the American civilizations, not counting the "Big Three" Inca, Aztecs, and Maya.
I also suggest the Australians because that continent needs to be filled out, and if the Aborigine don't make it in, then Australia is a good choice. Hey, America made it in ^_^ I still say the Aborigine would be best though.
