I started playing the witcher 3 wild hunt after Christmas. I know the game has been out for awhile now but my question is what is the best time to start hearts of stone or blood and wine? I'm on my NG+ run through and don't know if I should beat the main story before or after getting the dlcs. What do you think is the best way to play.

They are stand-alone story lines, however the dialogue will change a little depending on whether you do it before or after you finish the main story. Doesn't matter either way, most people do them after.