I think the obvious answer is patrice bergeron
I think the best measure of two way is plus minus...
In his entire 10 season he has only gone negative once and last year he led the league with plus 36
thats like not even real... PLUS THIRTY SIX
he also won the selke because of it, on top of it he consistently leads the league (or is in the top few) with faceoff win percentage, hes been around 65 for three years in a row
And to top it all off and to make his plus minus even more impressive, he is one of the league leaders in penalty kill time,
P.S,
I have nothing but respect for phil kessel, but in seven years in the nhl he has only 6 positive years, granted his one positive year he got a 23 which is damn good
Of course Pavel datsyuk is also great, he is usually way up there for steals and plus minus, (also his best year he went plus 41)
so its between datsyuk and bergeron, but I think bergeron takes it