Well, both reels have their strong points. The Penn's parts are much more readily available than Shimano's, but you hardly ever need parts for the Shimanos because you can just send it back and have Shimano fix it for you (or replace it). Penns generally have stronger drags, but I've never been in a position with my calcutta where I wished I could get more drag out of it (this is a small reel, so you don't need a whole lot of pressure anyway). One weak point of the Calcutta is the roller bearing. It will rust quite easily, but if you keep it lubed and rinsed it should be fine. It's fairly easy to fix if it does get rusty, so I don't mind it that much. You can literally fix a seized roller bearing quite easily, so it's not that big of a deal. Different people have their different opinions, some people hate Shimano and love Penn, others hate Penn and love Shimano. Personally, I've been very happy with all of my Shimano products (barring the Corsair, but they did replace it when it crapped out) and have no reason to switch to Penn (the only exceptions are reels like the jigmaster, 4/0, 6/0 etc.). I'd suggest Shimano over Penn, just because both reels are very similar, but in my opinion the calcutta is a little bit smoother, casts better, and the customer service is literally second to none.
-Brian