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I would say that synopsys is the first one and then cadence PKS. The graphical interface of PKS is not very efficient! the cadence tools may be faster thansynopsys, but the netlist produced by synopsys is better in timing & area.
There is no point to do a synthesis or even a physical synthesis without any constraint! The constraints are probably the most important thing and the most difficult task during the synthesis.
Both ambit or synopsys can produced a netlist without constraint. In that case it's just a RTL to gate translation.