I will tell you my favorite lilac, which is the limited edition (spring 2012) Jo Malone White Lilac & Rhubarb, now out of stock in stores but I am seeing it online at the Malone website (see: http://www.jomalone.com/templates/pr...T_ID=PROD17366)
This is a breezy lilac that gives one the impression that one is standing in a yard smelling lilacs and greenery on the breeze.
If you don't like the idea of a limited edition that will not always be available, here are two that many like, which have a lilac note but are not soliflore (single flower) fragrances:
Frederic Malle En Passant (smell this one at Barneys or Frederic Malle, or Aedes de Venustas in NYC; Aedes has a sample program by mail of 7 decanted 0.7ml glass vials for $15, of which $5 is applicable toward a purchase of one of the perfumes sampled, see: http://www.aedes.com/Aedes-Sample-Service_p_908.html
Ineke After My Own Heart (you can get a set of 1.5ml samples from Ineke's website for $25 including shipping, which is fully applicable toward a full bottle, see: http://www.ineke.com/catalog/product...products_id=39 )