I thought you'd go for ANTARSYA.
Anyway still Syriza, who have been pretty dreadful and incompetent but I might as well protest ineffectually. ND and Pasok are client-driven machine ideology-free piles; Potami is a dull media born celebration of vapidity; GD is literally Hitler, ANEL are metaphorically Hitler, KIDISO is a one-man band of a political failure, Union of Centrists are a silly vanity act and KKE are a cult.
Perhaps I would throw a vote at an Animal Rights Party or some minor ecological grouping if Syriza does something silly, but might as well throw in a bit of solidarity if they still exist.
ANTARSYA is more or less SYRIZA but with more street cred, imo. I don't have any illusions in the KKE program (which I think is nationalistic, simplistic, and frankly kind of dull), but they are the only party putting forward a 'class against class' line in Greece right now and as such, I think they deserve at least some critical support from the Marxist left, especially against proven reformists SYRIZA and PASOK. But in the end it doesn't really matter, because I don't think the fate of Greece will be matted out in the bourgeois parliamentary circus, but rather on the ground. IMO the most important thing at the moment for the Greek Left is to forge a Bolshevik-Leninist vanguard party that will overthrow Greek capitalism rather than attempt to manage it. If that is going to happen anywhere at the present time, it's going to be in Greece, so I'm optimistic, but that party won't be the KKE, SYRIZA, ANTARSYA, etc. It'll likely be a new development that comes out of this collapse, and, if a party of that caliber does not arise, the end result will be fascism or military dictatorship.