I also like Yuan Shu, and on the contrary, I really dislike Yuan Shao's and Gongsun Zan's. Sun Jian's was disappointing too.

Of XII I like Diaochan's alternate portrait:

Lady He is quite nice:

Sima Shi's portrait looks good too:

And Zhang Liao always gets special attention from Koei. Again nice artwork for him:

From XI I guess my favourites were:

Diaochan:

Lady Huang (I like her simple look in this portrait):

Hua Xiong (seems more fitting than his XII version):

And the action portraits were cool:

File:Sun Shang Xiang RTKXI Action Portrait (Wu).jpg

not too shaby

Anyone know how to unlock more potraits on this game?

Thanks in advance!

You need to have "seen" that person. I once had Guan Yinping in my kingdom, but I never had any interaction with her (never talked with her, never appointed her to minister, never controlled her during battle, etc), so I never unlocked her portrait. However, I did once organize a banquet in a city that wasn't mine, and Sima Zhou came there, and so I unlocked his portrait (he wasn't even on my side).

So, basically you need to see the portrait in-game to unlock it.