I will be willing to brave the wrath of the Festoolians (even though I own some Festool-s) and disagree. The 6" Porter Cable VS sander is top notch and I would put it up against the 150 any day of the week.
I'll actually second that. I had a boat builder friend who bought the rotex based on my recommendation. He wasn't that impressed after using it for a week, went and got the PC to see if there was a difference, and after another 5 days and tests that I dropped in on after hours with each sander, he sent the Festool back for a full refund (kudos to festool taking it back). For him it was about speed in random orbit mode, and the PC was considerably faster and left the same finish using the same papers.
Also when I was attending a certification course for Solid Surface work, the instructor swore by his rotex (it was just like mine and at the time I felt special because there were so few of us out there then). Half way through the first day his Rotex died! and he had to finish the rest of the seminar going to his backup, an old PC 6" vs.
My Rotex also died a month after the 3 year warranty period was up (good German precision, eh). I took it apart and discovered lots of carbon build up, real dark dust. Blew it out, checked the brushes, which were fine, put it back together and it worked again. It is still going, but when it finally dies I doubt I will replace it with another, and probably go the Fein or PC route.
So, those are some examples that showed I may have wasted some money, and some rare lack of praise for Festool. All that being said, the ES 150/3 is my favorite orbital sander of all time, and the vac is an excellent design. My boat builder buddy did keep the vac, too. Now if they could make some square drive bits to work with their chuck systems.