I would be more likely to say "I need freedom in my life," or "I need to be/feel free."

I agree with Dan. Good answer. Liberty has a political/philosophical sound to it where freedom doesn't. It would sound a bit weird to say "I have liberty in choosing cell phone plans" - you could say "I'm at liberty to do what I want" and that's ok. Or "I'm at liberty in choosing cell phone plans" but freedom is a better all round word in an informal, non-political sense.

When in doubt, choose "freedom." "Freedom" is a plainer word and covers a wider range of situations. "Liberty" is a loftier word that is more likely to be used to describe ideals, or in reference to groups of people or nations. The two words are almost synonyms, and the meanings overlap. I can't think of an example where one would be right and the other actually would be wrong. In the following sentences, either word could go in the blank, but "freedom" would be more likely in example #1 and "liberty" would be more like in example #2. 1) Our cell phone plan gives you the ___________ to choose between ten different plans, whichever is best for you. 2) The founders of the United States wished for the blessing of __________ . This is a good example where English has two similar words, a plain one ("freedom") derived from an Anglo-Saxon root, and a fancier one ("liberty") from French and Latin. P.S. I just found a long and thoughtful essay by an English language expert on the ways in which the meanings of the words have evolved over time in the United States: http://tinyurl.com/zu8rl4f

You can use them interchangeably in a sentence like that, the only difference is that you can say "I am free!" but you can't say "I am lib!"