I own a Houdini, and kinda want a POTC (I call it Princesses of the Caribbean because they sugar-coat the portrayal of pirates big time. Pirates were the terrorist thieves of their time.)
I refuse to say which 'is better' because that is difficult and likely inaccurate. However, I like Houdini because it is a fun, difficult shooter with a boat-ton of code goodness. It's like they took a nice B/W game and gave it a decent, non-trival ruleset. Score!

Now POTC, on the other hand, is a bit more expensive...but you get a beauty of a machine for your money. It also looks like it has some serious deep rules, likely more than Houdini. Kind of a longer player, like LOTR. Soooo many shots. To summarize, this looks like an adventure pin.
I like both, and side by side, they would be great in my collection. A buyer should consider what kind of experience they want out of a pin rather than which is better. These games are far too different for that simple comparison (IMHO). These aren't System-11s.

Go Pinball!!