1. would be the sentence used. This is because 'rational' and 'reasonable' are close in definition, but different in tone.
The difference is that if I say something is reasonable, I would say that a person who disagrees with me is being unreasonable - they are considering all the arguments.
If I say a solution is rational, it implies that any other solution is irrational - a term that implies a person is not thinking clearly at all, either because they are mentally unstable, very angry or under the influence of some drug. The mental picture of an irrational person is much more negative than that of an unreasonable person.
The difference then, is in the respective opposites of each word - the image I would get if a person were not being reasonable versus the picture of a person not being rational.