I would say anything orange in the first 12 levels.
I was lucky to get my first legendary killing Lavender Crawly at level 9. A cash infused Bitch. I was so excited to see it at such a low level. It lasted well into level 15 for me.
As for an Anarchy, you have to get to DLC2 GLT for that one, and while it might have been nice for it to be a world drop in the regular game areas, Gearbox was wise to make you buy the DLC for access. Once stacked, it is one of the best shotguns in BL3, just watch out for back splash!
Have fun and good killing!