Honestly, as with anything like this, it depends. A being that understands love can use it to great effect to manipulate people, but might also be able to be reasoned with. A pure evil being would not be so good at manipulating people, but also couldn't be reasoned with. Assuming they both have the same level of power, I would personally say 'sinister, but understands love', though if they are immensely powerful, to the point of being able to wipe out any opposition with ease, pure evil is probably worse, since at least someone who understands emotions like love might be possible to reason with..