Their are so many questioned not being asked or answered first that could answer all these questions. Questions like:
What is your chord rate of change?
What is the style?
and more importantly
What chords do you feel should be there?
I can tell you all the theoretical things I have learned about how to harmonize a melody, but only in the context of baroque and classical era music. I can show you how the melody itself suggest the harmonies to use. However, these things will only guide you so far before you are back here at square one again. Because in the end, the choice is yours and yours alone. You can literally do and choose what ever chord you feel needs to be there. You are not bound to any rules of harmony and no one will think less of you.
So unless you are trying to write in a specific style of either baroque or classical, or this is for a music theory lesson, I would not worry so much about which chord you are using in your own music, but first write down what you want to be there and work from there.