Hi bro, you can use either distilled or RO/DI.
But as to which one is more of a hassle ... a bit debatable.
using RO/DI - you can get the water as and when you need it. do not have to worry about stocking bottles of water. But need to change resins and media from time to time.
Leveraging on distiiled water which is about 45 cents per 1.5l during special offer days, it could be cheaper with no startup cost. But you would need to carry cartons of bottled waters back from supermarket to your home and also find place to stock them up. Then for water change,you will need about 7 bottles for a 20gallon tank. If you do it weekly, then you need about 28 bottles per week and you still need to buffer some bottles for topping up daily.
This should give you a good idea of how many bottles you need. (unless if you are ordering those commercial distilled water - large large container ones that are being sent to your place.)
hope this help.