The extra GSO cost of Maduin hurts. Between that and the fight over GWOs I'm heavily considering just honing Alexander at the moment since few enemies resist/absorb Holy, and whenever it comes up there're always r5 3* summons that could be useful in its place.
Don't know what 5* abilities I want to make yet... Bahamut and Odin seem unnecessary at the moment and I don't want to take up an ability slot for a single use. Meteor could be good to have, though Ruinga is coming and is easier to hone. Full Break I'll be creating for sure and Meteor will probably depend on how well Ruinga works on high difficulty trash waves. The only other current ones that look good are Barrage , Quick Hit, and maybe Entrust, but Barrage uses MWO as well as MPO and MEO used by Meteor and Full Break, Quick Hit has a ridiculously expensive orb cost, and Entrust would be pretty situational (I'm thinking of using it with Cloud's RM3)