There has been a little bit of a debate about this, which occasionally turns into a troll/flame/FUD fest.  People are very defensive about their coins.  Personally I feel that SDC has the most promise from things I have seen. However I think we should support all projects that are attempting to increase privacy and anonymity in crypto.  

Anyways Isidor Zeuner is said to be coming out with a review on ShadowCash in the near future, and I heard he may also be comparing ShadowCash to Monero, DRK, cryptonote, and other anon coins to highlight the similarities and differences.  There has been some confusion on this issue.  I think that if ShadowCash passes peer review without any critical flaw then it is probably the best anon coin.  But I'm sure others who are diehard fans of other anon coins will disagree.

Also I should mention that the Shadow Project has other valuable things such as ShadowChat encrypted messaging within the official wallet.  Soon they say they will add voice, video, and file support.  They are also working on a decentralized marketplace within the official wallet, similar to open bazaar.  They also have had many other accomplishments with their wallet and mobile wallets.