I have not been to Vertigo, however, in review that I have read is has a better view (farther from the cluster of high rises); however, the food is better at Sirocco. In my opinion the food at Sirocco is better than average but at a very very premium price. Much of the food offered is Western.
On my last trip to Bangkok I took a date to the Blue Elephant restaurant which is in walking distance from Sirocco / The Dome Bar. We went to the Dome Bar after dinner and it was a great combination.
Blue Elephant Bangkok Restaurant and Cooking School is a very fine restaurant with prices lower than you would expect. Great service and atmosphere.