Sirens are beautiful mythological creatures that lure travelers to their destruction through song. Sirens sing to those who travel by sea in order to guide their ships into rocky waters, causing them to wreck and drown.
In the Odyssey, Odysseus orders his men to plug their ears with beeswax so that they will not be tempted by the voices of the sirens. He asks them to tie him to the mast of the ship, but to leave his ears unplugged out of curiosity. Odysseus hears the following song:
We know all the pains that the Greeks and Trojans once endured
on the spreading plain of Troy when the gods willed it so--
all that comes to pass on the fertile earth, we know it all!
This strange appeal to knowledge causes Odysseus to beg to be set free; thankfully, his men ignore these pleas, thus, ensuring their safe passage.
On the other hand, the lotus-eaters cause trouble to travelers by providing them with lotus fruit, which causes those who consume it to think only of eating more and to forget about returning home. Odysseus must drag his men off the island in order to escape this fate.
Overall, the sirens seem to serve up a worse fate than the lotus-eaters. Although encounters with both creatures will eventually lead to death, following the songs of sirens means that death will be far more immediate.