It takes a lot of energy to hate enemies, and it causes a lot of physical and emotional stress. The time spent plotting revenge instead of creatively going about one's day is prohibitive. Loving our enemies instead of hating them promotes an almost superhuman strength of will. By loving our enemies we can develop those qualities within us that make our lives happier and more successful.
It is not an easy thing and unless you are the Buddha or Jesus you are not going to do it very often, but it is best to love our enemies and only hate the things they might be doing. That is the enlightened way and it ensures that you do not become like your enemy.
Yes, I think we should love enemies rather than hate them. Hate is an extremely negative emotion. It takes more energy, emotion, and concentration to hate a person. Hate takes away from a person's ability to enjoy life. Left unchanged, hate will grow like a cancer as long as you continue to feed it. By letting go of hate and loving your enemy you let go of the negativity and find that you feel much better inside.
In a black and white word it may be easier to love your enemies rather than hate them, but I think that sounds pretty naive, in my opinion. The real world has real consequences and sometimes your enemy is out for blood. Loving them is not going to stop a weapon.