Well, what do you like? What would you not tire of seeing many hundreds of generations down the track? Are you about visual appeal, or do you like utility functions?
You can have a look at the Rare Breeds Poultry Trust to see what's on the list.
However, if your magpie project failed because of difficulty in sourcing appropriate stock, that's going to be a common theme in re-creating or rescuing any of the rare breeds. Getting the stock to kick-start the project, and then sourcing suitable stock to strengthen the genetics part-way through, without significantly impacting the work you've done to that stage, is always going to be somewhat fraught.
I actually do think there's a lot of scope for working on blue/green egglayer breeds. There's only two purebreeds certified for that eggcolour (Arauacana and Cream Leghorn), while there's hundreds for the white/brown breeds - in utility breeds alone, if you specify "excellent layer of bright white eggs", I can think of three breeds instantly off the top of my head (White Leghorn, Ancona, and Campine).
So "excellent layer of bright blue eggs", starting with one of the major white egglaying utility breeds and the best blue egglaying Araucana one can get one's hands on, isn't such a bad concept to try and create a purebreed from.
My opinion alone, of course, because I like all the pretty egg colours
