If you want the most fun, get a BMW 530i with a 5-speed. They are so tight!
BMW 5s and Lexus GSs are so common, that I think both have the same level of "flash factor." Meaning, a woman would turn her head equally as much for both cars.
The Lexus, however, would be in the shop less and you would probably have a better buying experience with Lexus. I test drove an IS300 last week, and the day after I received a letter from the salesman, thanking me for visiting. During the test drive, there was no talk of purchasing at all; I just asked if I could drive it, gave him me license, and he handed me the keys. They gave me a good impression.