i played ac:brotherhood having never played any ac game, imo was a great story game.
imo i'd do ac:brotherhood over kotor2. played both kotor 1 and 2, well played them both 2 or 3x (of course to try both light and dark) kotor1 was definitely way better than kotor2, i'd say kotor1 is like 95% and kotor2 is 85%, of course kotor2 has some upgrades and saber customization, but the story just "felt better", plus when you finish kotor2, you'll be like, this is it? it feels so... unfinished. This is of course compared to kotor1.
i know ac:brotherhood isn't on your list but i haven't played ac1/2 so i can't compare that, but my finacee saw me playing it and even bought it for a friend cuz she thought it was so cool.