If you want only one herb in your kitchen garden, plant spearmint.
Spearmint may just be the easiest herb to grow; all it needs is average soil, sunshine and water.
Once established, it's hard to kill and, like many herbs, needs help staying contained.
I have spearmint planted where I can easily reach it.
Spearmint makes a great garnish and accent, especially for fruit dishes. It's such a versatile herb, I also use it in the garden when I need a bald spot filled in.