I suspose it may depend what is important to you. The Universal is bigger with a better res screen and is a more mature product, so hopefully most of the bugs have been ironed out of the ROM. Hermes is smaller and has high speed 3G.
Well, as the Hermes is newer (even if not more powerful), I would hope it was a more mature product in its own way. That said, they both run Windows Mobile 5, from what I can tell.
I currently have an SPV C550. I've had a play with the M5000 in shops (well, a dummy model) and it never struck me as fitting into the "too big" bracket. I definitely want something with touch screen and a keyboard -- surfing the web with a "normal" sized phone never felt particularly comfortable.
However, both the M5000 and M3100 offer this
Arrrrgh, why can't these things be simple
I suspect I'd rather go for the bigger screen and enhanced processor power though.