There are two specific dairy-free butters that I love.
The first is Smart Balance Buttery Spread-Light with Flaxseed Oil. I like this DF butter because it tastes great, is relatively easy to spread right out of the fridge, has 0g trans fats and has flaxseed oil in it! On the downside, it is not the easiest to bake with. It makes cookies spread too much and breads and cakes fall apart. It's almost too light for baking needs. Sautéing wise, it's great and adds a nice, light buttery taste to pan cooked meals.
The second DF butter I love is Earth Balance Buttery Spread. It is available in a soy version or soy free. I choose the soy free version because I try to watch how much soy intake I get daily. (There's been studies out that say women in their child-bearing years should limit the amount of soy products they consume as it can affect their reproductive hormones while women in their menopause years and thereafter may have as much soy as they like as it help with the hormonal transition.)
Earth Balance Buttery Spread is so easy to bake with that you would never notice the difference in cookies, cakes, or breads. At room temperature, it does get really soft and can be difficult to work with in frosting recipes. (Soon to come..... my yummy Buttercream Frosting recipe that has gotten rave reviews and is stable at room temperature, buttery, dairy-free and delicious!)
So if you are baking, I would recommend Earth Balance Butter. Where as if you are cooking on the stove or buttering a slice of banana bread, you can use either. Good luck in your dairy-free ventures!