Currently I'm mining Siacoin as it appears to be the most profitable given my computer specs (SLI 980 Ti, 32GB DDR3 i7-4790K). I think due to it's relatively low cost and difficulty, it could be very profitable in the future depending on well Siacoin itself does.
I'm currently pulling around 3000-35000 MH/s depending on the difficulty and my overclock which gets me around $11 USD worth of SC a day, and given that SC is currently 0.01-0.02 cents per unit, that's quite the number of coins to have mined.
Siacoin itself seems to be very young, so I don't imagine you would be able to mine a lot and sell them for a good profit in the short term, I think this will be one of those coins you mine as much as you can, and hodl for as long. Not to mention once they get their storage system fully working it'll be pretty viable to have a good supply of SC on hand