Look, if it’s someone’s first time watching, then 4,5,6 then 1,2,3.
If not, then do it whatever way sounds best to you. I try and never do the same order twice in a row. I think there’s merit in each way of viewing. My favorite is the machete order if I’m just watching by myself, but seriously it’s whatever way u wanna watch them, man.
In preparation for TFA I did them in numerical order.