Nat B, I use what I can get... at Sprouts near my house usually.
Romaine is considered mild.
I get dandelion greens (don't use the red dandelions myself, either I didn't like them or they gave me problems, don't remember?).
I don't like mustard and turnip greens, though mustards are supposed to be good for inflammation if I remember? Too spicey for me, could only take tiny bits so I don't like to buy a whole bunch and waste it.
I don't like arugula but some crave it. It smells bad to me; I listen to that.
Parsley - I like it and it's great detox.
Beet greens -- buy the beets and use the greens or eat in salads. I prefer red and think my body craves them. Gold beets really do nothing for me and the rainbow/white or stripey ones as well... but the greens seem the same with any color. I look at them as free greens because I buy the beet roots in bunches for less than buying them without greens.
Some here use fennel and I've tried it and bok choy.
Don't forget cabbages - some juices have that in them.
Last Summer as a cost aide, I bought a good bit of watermelons on sale, and stripped the red fruit for others to eat. I juiced the rind to add volume, as a sort of carrier for our green juices. (We had 3 here on juice fasting at a time.)
Don't forget you're getting greens in the peels of cukes for instance. Some people use broccoli.
Oh, and we add a pound of green beans to green juices sometimes -- I tried adding 2 lbs once and it was too much.
Really, amongst what I add in, I just cram as much in there as I can get in to green juices.
See you over on the groups, hopefully.