Depends on what you mean by 'nice'. I'd like to say that I always try to be a decent-hearted, honest, open and kind person. But I feel there is a distinction to be made between 'niceness' and 'kindness'. Niceness, by its definition, is inoffensiveness; it's ultimately doing or saying what you feel you're supposed to do. You're nice to your bus driver, waiter or a stranger on the street, and it's good to be polite. But you should be honest, open and true to your friends; and sometimes that requires you to be tough or - not unkind - but telling them things they don't want to hear.
I believe kindness is doing what you feel is right, what you want to do. A kind person gives money to charity because they want to, they sit with someone who is lonely and talk to them because they get joy from helping others, and expect nothing in return. A kind person tells someone what they feel they to need to hear, not what they simply want to hear, because they believe the truth is more important and helpful than being thought of as 'nice'. Nice people will often say things like, "Oh, I feel bad for old people sitting by themselves", "Oh, I'm always sad when I see the homeless" over Facebook, rather than doing anything out of their way to help those people, so they can inform their friends they're "so caring".
'Nice people' are often insecure. They don't say what they really think, they don't assert themselves out of fear that people may not like them. Nice people are guilted/cajoled into doing things they don't want to do, and then feel used, whereas a kind person will help who they want to help, when they want to help, and not allow someone to manipulate them in that way. Nice people expect things from their 'nice acts' (hence the much detested 'nice guy'), a kind person expects nothing in return, merely the pleasure of having given or done some small good.
I admit it: I was a nice person. But now I hope to be a kind person; not sure if i'm quite there yet.