It depends on everyone's particular possibilities...:
COMMERCIAL: Virtuoso, with XL is greate, but without it is also a powerfull tool.
OPEN/FREE: LASI. I used it almost 10 years ago (I'm sure now it should be totally different and better) and I remember it as something owesome to be FREE!!!!
I used SX9000 and AlphaSX by Seiko Instrument before but now Virtuoso by Cadence. I'd say they are both good with one having some advantage over the other...
anybody using tools from other makers such as Sagantec or Magma?