The performance in normal usage of all SSD's is remarkably similar.
At equal capacity, Intel 520 and samsung 830 are very similar in performance.
One big determinant of performance is how much of the drive you fill. As the drive gets filled to near capacity(80%) updates take longer; perhaps significantly longer.
Therefore, to answer your question, the 180gb drive would be much better. It is absolutely much better if you intend to put as much as 90gb on the drive, in which case, the 120gb drive(110gb useable) will not be so good.
Today, I would stick with Intel or Samsung for reliability. They make their own nand chips, and can do a better job of validation.