In the miniseries it is said that there was 12 original Battlestars, one for each of the 12 colonies of man. We know that Galactica of Caprica was one of them. Do we know any of the other twelve and what colony they represented? Was Pegasus considered an "original" Battlestar?
The short answer: There is no official list
Perhaps this is a question best left unanswered.
Here is a transcript of a dialog recorded at the Galactica 15 Yahren Reunion, between Glen Larson, and an inquiring fan (actually, Larry Mager dressed in Commander Cain garb):
Fan: What were the names of the twelve battlestars? We've seen different lists.
Larson: They weren't battlestars. They were the names of the planets.
Fan: You have the Galactica, the Pacifica, the Atlantia, the Pegasus... the ship names.
Larson: We never arrived that there were twelve battlestars. We only actually shot the Atlantia, the Pegasus, the Galactica. I can't think of any others.
Fan: During the attack by the Cylons on the fleet, you hear in the background, the Pacifica, the Triton is moving up alongside the Acropolis. You hear these different names coming up. And we are tryng to decipher what they were.
Larson: I appreciate the question and we have reason to want to look into that, and we'll have to research that.
A partial list can be constructed from the dialog in the premier of the original BSG; several more from subsequent episodes.
From the Wikipedia entry on Battlestars:
Galactica, Atlantia, Pacifica, Triton, Acropolis, Pegasus, Columbia, and Rycon are all mentioned on film.
Solaria, and Cerebus are mentioned in the novelizations.
Prometheus was on a list given to the production department.
That makes 11 mentioned in OBSG sources. We don't have a canon affiliation to given colonies, either. Adama heads for Caprica because it's home to him... to try and rescue his wife.
The Galactica is one of the original 12, according to the miniseries.
According to the Battlestar Wiki, 3 are known from the nBSG video: Galactica, Columbia, and Athena. These belong, according to the designer (as quoted in the wiki), to the Jupiter Class, which means we know 4 of the 12.
The Pegasus is not of the Jupiter class, which probably rules it out, as the Mercury class is newer. It might, however, have been a replacement for a Jupiter class Pegasus.
Twelve colonies/tribes are mentioned, and yet, we see only five flying in formation during the opening credits. Five Battlestars and no screening or escort vessels. Also, logically we should discount the PEGASUS as it was thought lost, while under the command of Commander Cain in some battle in the past. It was a surprise to all aboard GALACTICA including Adama, who presumably was old enough to have remembered, or even served with him. Cain did seem to remember Adama as a fellow Colonial warrior. Also, and forgive my 64 year old memory, wasn't the Colonies at war with the Cylons a thousand year's war, which ebbed and flowed over time. In any case the battlestars would have had to be part of different classes. They wouldn't just keep cranking out the same class. As new technology was made available it would have to be integrated, and over time the frames would need to be replaced. So it stands to reason they would have different classes.