Modifying Glock 17 new or old

[mcgin014]

I currently have a Gen 3 Glock 17 2 pin frame and am drosing a new gen 3 17. I already have a Vortex Viper and suppressor sights that need to be installed. I can't decide if I should have my old Glock milled or the new Glock. I'm thinking the old one will be milled but want some insight on which I should get the work done on.