If you are only ever going to have one herb plant in the garden I suggest Lemon balm. It is reputed to have many health benefits, such as improved sleep, relaxation and helping with gut health.
I would recommend keeping in a tub, because it grows very strongly and will spread everywhere.
It’s recommended that you take one to two cups a day.
Pull off the individual leaves and don’t make the mistake of breaking off whole stems like I did. This will allow the little leaf’s to grow back. Wash the leaf’s well. Either put a number of leaf’s into a cup and pour on boiling water. Alternately put the leaf’s into a pan of boiling water and simmer for 5 to 10 minutes.
There are currently studies going on to see if Lemon balm helps with Alzheimer’s. The signs are encouraging.
This plant I have taken a picture of is green. But at my other house I had a yellow plant, that looks nicer.
All the best