Paint Tool Sai and PhotoShop are known to be the "big deal" digital art programs (and for good reason, because they have lots of cool components), but you can find similar programs. I, for one, love GIMP, because it can do many of the things photoshop can, and honestly, I found it less confusing xD. However, it's not pressure sensitive, you have have a tablet.
I just got FireAlpaca 2 days ago, and it's great for making smooth lineart (you can set it to correct the smoothness of your lines), and it's pressure sensitive, so it works well for painting hair and fur.
But like
>>2 said, when an artist works hard and practices, they can make good art on any program. (Though nice technology never hurts :P )