I have stayed at both, see the reviews of both properties here on FT:
https://www.flyertalk.com/forum/acco...l#post27759134 and
https://www.flyertalk.com/forum/acco...l#post27707496
The Pullman Naithon Arcadia is not just "a little nicer" it is a lot nicer (but commands higher rates, sometimes too high IMHO). That said the Panwa is not bad at all. It's a matter of personal taste I guess.