Of course it's Pienaar.
Arteta is first with 41, Baines second on 39, Pienaar 35, Cahill 31, Osman 28.
Baines and Pienaar have both played the same amount of years, with Baines on 204 apps and Pienaar on 156, giving Steven the better games/assists ratio of the two. Arteta however is very slightly ahead of both ratio wise with 41 in 174.