What a great question! I believe in unconditional love and in fact I believe that anything else isn't really love.
The opposite of unconditional is conditional, so if your "love" is based on certain conditions being met, is it love at all?
We absolutely need certain things from others - respect, intimacy, openness, a sense of safety. But if I base my "love" for someone on deriving things from them, that is conditional love. For example, if I require material wealth or 100% of their time, or if I require them to not do something like see their friends or family; or if I demand that they adhere to my beliefs instead of their own; or if I demand that they like the things I like and not the things they like; these are examples of conditional live. Love then becomes a contract based on their behavior and not on the feeling I have for them.
I love my dog, unconditionally. I love my children unconditionally, and there is nothing they can do or say, or not do or say, that could make me stop loving them. This doesn't mean I have to like all the things they say or do; it just means that when that happens, the underlying love I feel is unchanged.
I love my husband unconditionally. But in order to stay with him I need certain conditions to be met - I need to be safe, I need to be treated with respect, etc. While I would leave if these needs of mine were to be dismissed, I would not stop loving him, although eventually I think the love would not be able to survive being mistreated.
I love this question you've asked and I'm looking forward to reading others' responses.