I think some posters are getting confused by what the OP meant. I don't think the question was what wingers were the best at playing both LM/RM or what wingers were equally good going forward as they were defending.
A lot of wingers have a preference for attacking their man on the outside, whilst some are more comfortable cutting in. Valencia for example would always go on the outside of his man, whilst Robben mostly cut inside. As has been mentioned, Nani was difficult to defend against playing RW as he would cut inside or go round his man on the outside. Greenwood was also very good at this due to his two footedness and defenders found it very difficult to defend against.
Giggs in his prime was excellent at dropping a shoulder to come inside, beat his man for pace and carry on outside or across goal like the goal against Juventus or equally he would put on the burners and beat defenders on the outside.