I would, and did, take the No. 23. It sounds great to my ears. It may not be the latest in technology, but then again, it was Stereophile Class "A" when it came out, so it obviously is a very good performer. As far as looks go, how can you go wrong with Levinson. I actually like the very conservative look of it. It blends into the back ground, which the wife likes. Having double the power is a real plus. I used to have the No. 27, which also had 100W/ch, and it too sounded good, but I'll tell you, it is really nice to have all that power driving my speakers. If your speakers are very efficient, maybe you don't need it.
Since the price of the 23 is still less than the 331 (I believe), you might want to go with a 23.5, which is what I wish I had done, had I had the money. It costs about $500 more, which puts it in the same price range as the 331.
My two cents worth! Good Luck. I doubt you would go wrong either way though!