Marvel easily. Better writing and better acting in my opinion.
Flash, Arrow, Supergirl, Gotham, Lucifer, ect have their good episodes or moments but few of them are ever consistently good over a more than a few episodes in my opinion. To be fair those shows are stuck with the old fashioned 22 episode a season format which tends to dilute the quality of shows as they can't maintain overarching story momentum and have to make filler episodes.
Legends of Tomorrow is possibly the worst live action DC show on at the moment. The writing is bad. The characters are written as idiot screw ups that cause most of their own problems. The show is clearly limited by its budget which means characters simply forget they have superpowers or are written as not being able to use them regularly. It is also incredibly repetitive with characters frequently getting captured or trapped. It doesn't have anywhere near the creativity or imagination of something like Doctor Who.