Re: DFT tool
Cadence's Buildgates/PKS offers full scan-insertion and (if you have a PKS license), "placement-aware" scan-chain re-ordering. Having used both Ambit-DFT and Synopsys's DFT-compiler, I have to say DFT-compiler is easier to use. It's also more tightly coupled with Synopsys' TetraMAX (ATPG) companion tool (which my employer uses.)..
> Test Compiler is build in DFT tool in synopsys DC.
To clarify, Synopsys Test Compiler requires a Test-Compiler license. It is not 'free', as Synopsys still sells standalone Design_Compiler licenses. The program executable is packed in the same CD-image on Solvnet, but then so is Physical Compiler, DC-Ultra, Designware Foundation, and a bunch of other *expensive* add-on products.
I can't speak for the other tools, but Ambit-DFT is included free with Buildgates (no separate license needed.) If you have access to Ambit-DFT, you may as well give it a try. If your project is "DFT-clean", then Ambit is painless to use and will get the job done. On the other hand, if your project is not DFT-clean (lots of asynchronous set/reset flipflops, clocks not accessible from a primary-port, lots of custom 'macros', etc.) -- you will share my pain and find yourself making many RTL-code changes to accomodate Ambit-DFT.