Which one is a more desirable feature in an altcoin? The X11 or the Cryptonote? Also why cnt the 2 be implemented together? X11 seems to allow 11 algos to mine the coin, and cryptonote is based on something else.
''Which one is a more desirable feature in an altcoin?'' that's not an easy question and the answer depends on the philosophy you impart in your coin. X11 is in essence a PoW with 11 hash functions (blake, bmw, groestl, jh, keccak, skein, luffa, cubehash, shavite, simd, echo) if one of them gets cracked there's still 10 more to deal with. It does allow for reduced energy draw and heat output from GPU but that's pretty much all I could say about it's cons. The downside of X11 algorithm is in that it's not as long-term as some expect it to be. The experts claim that it will take a maximum of two years before this algorithm gets ASIC’d. Even though it’s complex, X11 is one of the mining algorithms which isn't relying on hardware memory hence it's much more simple to implement on ASICs. In my opinion all PoW algorithms need to use memory bound functions so if you are thinking long term I'd suggest you go with CryptoNight.
CryptoNight relies on random access to the slow memory. And a megabyte of internal memory is almost unacceptable for the modern ASICs. So far quite a few coins have been using this algorithm, all of them are CryptoNote-based. Bytecoin (BCN) is probably the most prominent one since it was the first coin to have built its architecture around the CryptoNote protocol. Bytecoin has been around since 2012 but from what I've heard the development started as early as 2009. It is a CPU-minable coin with anonymous transactions feature and immunity to ASICs. You could try mining Bytecoin with a GPU but the coefficient of performance would be comparable to CPU-mining. Bytecoin is doing pretty well and there are other coins with CryptoNight algorithm; Fantomcoin, Quazarcoin or Monero.
Theoretically you could implement X11 and CryptoNight together in a cryptocoin but two years later you'll inevitably face the ASIC problem for your X11 PoW. So I don't really see any practical use of such a combination.