X11 or groestl are both great. Groestl is even more efficient than X11 and allows some good cpu mining and is old gpus and nvidia friendly, kind of universal and really balanced algo, i love it afaic, very promising, see groestlcoin : https://bitcointalk.org/index.php?topic=525926.0.

N-scrypt is not that efficient, it's between X11 and scrypt in terms of power consumption.

With summer coming, better go for the best efficiency to keep miners motivated.