I find XCN to be a good stand-by for mining.
As comparing SIGT to XCN... XCN does pay out a bit more than SIGT currently (with my systems; its XCN $68.87 vs SIGT $65.84).
However that said, SIGT seems it will go up some more, and thus have better value (and currently can be traded), until the difficulty rises, Block 30,000 I believe.
At which case, then XCN may be the better deal to mine on a daily basis.