And Skipworth vs Swallow vs Mackay vs Coughlan vs Butler
None of the players you have listed their are renowned for durability, though Mackay and Skipworth played out the majority of 2008 at least.
Mackay and Coughlan are the only two I feel have good job security at the moment. Skipworth is an unknown, Swallow I'd say is probably more of a VFL player. Not too sure about Butler.
The safest option seems to be Mackay. Problem is he probably has the lowest ceiling of all the players listed. He doesn't get a lot of TOG (averaged around 60% from memory). Coughlan has the highest ceiling I'd say, being the most genuine midfielder, but he hasn't played at AFL level in two years, so I'm thinking he'll struggle for TOG early on (or may even play in the VFL to start). I'd personally go for one of Mackay or Skipworth.