It seems there is alot of argument of which coins are "better" though each have their pros and cons. One is more established, the other has some features promised with new technology. See below for the Pros and Cons i have found for each, if you can give me more to add to the list i will. But please provide sources to the information you are giving.
Cloakcoin:Pros:Trading volume is much higher around 3 times the amount.
https://coinmarketcap.com/Uses a architecture for anonymity. See PoSA, Point of Stake Anonymity.
https://mega.co.nz/#!1c9UnKBI!BdEaoBuYDAr5F4nwltpYjYNOrZt7Jretk07eGc-oPDcCloaktrade: Working on an exchange system built into wallet using an API code from Bittrex.
http://altcoinstrader.com/cloakcoin-cloak-announcements/Has a feature of Stealth Addresses.
http://sx.dyne.org/stealth.htmlPlans on having a built in Marketplace on the wallet called OneMarket
http://www.cryptoarticles.com/crypto-news/cloakcoin-development-update-onemarket-posa-oneledger-ciaraCons:Traded on fewer exchanges.
http://bitinfocharts.com/darkcoin/The developers are completely anonymous.
Cloakcoin ANN on Bitcointalk is self moderated, many critical comments have been deleted.
https://bitcointalksearch.org/topic/ann-cloak-cloakcoin-no-premine-x13-decentralized-market-and-posa-637704Very short mining period, Mining will stop after 10080 blocks (7 days).
https://bitcointalksearch.org/topic/ann-cloak-cloakcoin-no-premine-x13-decentralized-market-and-posa-637704Dark Coin:Pros: Is more established, has been around since January 2014.
https://bitcointalksearch.org/topic/anndash-dash-dashorg-first-self-funding-self-governing-crypto-currency-421615Has a higher Market Cap of currently 20 Million dollars.
https://coinmarketcap.com/Very low bloat in the blockchain.
http://wiki.darkcoin.eu/wiki/FAQ#Is_Darkcoin_going_to_implement_ring_signatures.3FA higher network hashrate.
http://bitinfocharts.com/darkcoin/Is more commonly known in the crypto community and social media.
http://topsy.com/analytics?q1=darkcoin&q2=cloakcoin&via=Topsy
Cons:Was instamined over 2 million DRK on launch, due to only a few having access to the windows mining client and not publicly released for some time. And due to problems with the difficulty readjustment.
http://wiki.darkcoin.eu/wiki/FAQ#Was_Darkcoin_Instamined.3FXCurrency:Pros:Known dev team
http://xc-official.com/the-xc-team/Decentralised trustless Privacy in several layers,
https://bitcointalksearch.org/topic/xcxcurrency-decentralised-trustless-privacy-platform-encrypted-xchat-pos-630547Encrypted messaging XChat
https://bitcointalksearch.org/topic/m.8119953multi-path implementation that employs multi-sig to route fragments of transactions down separate paths through the network, compounding anonymity while adding redundancy and security
http://www.cryptocoinsnews.com/news/xcurrency-unveils-cryptographic-privacy-technology-wake-nsa-xkeyscore-outrage/2014/07/04Cons:Premine of 125k (2.27% of all coins to exist in the form of a premine)
https://bitcointalk.org/index.php?topic=630547.18800ANN on Bitcointalk is also self moderated (after unmoderated thread turned into a fud fest, so requested by community)
https://bitcointalksearch.org/topic/xcxcurrency-decentralised-trustless-privacy-platform-encrypted-xchat-pos-630547Supercoin:
Pros:Supersend feature
http://cryptocoins.co/supercoin-supersend-featurePOS superblocks
http://cointelegraph.com/news/112195/supercoin-a-trustless-decentralized-anonymous-p2p-networkCons:Supersend based on Coinjoin
www.super-coin.net/SuperSend.pdf