There are a lot of reviews of IB J on this board.
The new J cabin (all the A330 and most of the A340) is a better seat than BA's CW. Opinions on food differ (I like it), but the lounge in MAD is very good with hot food options and you can eat before flying.
Unfortunately, it seems that most days the MAD-PTY route is flown by the A340-300, with the old cabin (which I have not experienced). When is your flight? IB is receiving new A300-200 late this year and you might be lucky. Anyway, it is not that uncommon to send the A330 to PTY, although you should know that IB makes frequent plane changes, so seeing an A330 in your booking is no guarantee.