My dear Lalage, you definitely need both!
I have and love both also. I tend to reach for and enjoy Chloe Narcisse in bright warmer weather as I find it very feminine and tropical. It is a spring and summer staple for me.
Moschino by Moschino, is very rich with a seductive rosey amber musk drydown that I appreciate most on crisp autumn and colder winter days. I find it way too intense / cloying for summer wear.
If you must choose only one then I would say to buy the Chloe Narcisse as you will get plenty of wear from it in the coming seasons and get the Moschino at a later date, in preparation for autumn / winter.
Either way, you are going to smell gorgeous!