I heard the HORI Battle Pad is a better alternative than the PDP Fight Pad. I can't vouche for either one since I personally have never held either, but it seems that every reviewer likes the HORI Battle Pad more. I believe it was due to the feel and responsiveness of the controller. The PDP Fight Pad, of course, is better aesthetically. I absolutely love my Pro Controller... mostly for other games such as Hyrule Warriors or Mario Kart. I do like it for Smash but the ABXY button placement is a bit low for me. I wish it had been higher. The C-Stick isn't too badly placed... my only concern is the lack of grip it has and that I find myself touching the C-Stick accidentally when playing Smash since it's a bit too close to the ABXY buttons. There is also the lack of an octagon carving where the analog stick is placed, which many have mentioned. Without one, I find myself doing miss-inputs with certain characters (Shadow Sneak accidents, Zelda/Palutena Teleport inaccuracy, etc). However, the Pro Controller seems very responsive, with little to no noticeable input latency. I recommend it as a great alternative to the GameCube Controller. Plus, it is wireless with 80 hours of battery life and it doesn't take that long to charge. It comes with a USB charging cable that you can connect to your wall if you have an adapter (Like your phone charger), laptop/computer, TV (I assume it can charge from there), and even the Wii U console. You can have it charge on your Wii U console while playing Smash, which is great since you'll never have to put down the controller.
But regardless, I'll eventually purchase the GameCube Adapter and 2 new controllers since it'll always be the definitive way of playing Smash.