Are the current leaders of the FMLN socialists in the Chavez/Morales style or the Lula/Bachelet style? They seem from the Wikipedia article to have had a lot of factions on both sides.
The FMLN's presidential candidate, Mauricio Funes, appears to be more moderate, in the Lula/Bachelet mold. However, others in the party are far more radical, including vice-presidential candidate Salvador Sánchez Cerén. In the 1980s, the FMLN was an extremist terrorist group backed by the USSR. The party as a whole has moderated somewhat since then, but extremists still remain.
I feel like ARENA has done just as much "terrorism" as has FMLN. I put quotations around terrorism because it was a civil war, and while horrible acts were committed I don't think it is quite accurate to call it terrorism. Personally I see the FMLN as being center-left currently.