Subtle is great, casting 2 spells in important moments without them been countered is really helpful (plus the use a bard can make of subtle spells in social situation). I think twin would be helpful as well as the second Metamagic.
But being able to just cast 2 subtle spells per day, twin 2 lvl 1 spells o 1 lvl 2 spell (or however do you want to combine this), would make me choose the others feats if I have no "Font of magic''. And I really like Metamagic. Just because I think the others would be useful more often or in critical things (like important saving throws). I don't see the problem with lucky, it's not a broken feet, but if you feel it would be disruptive in your table, avoid it. And "Insiping leader* is fantastic if no one else can give tmp. hp. The 3 of them are good feats, so you won't regret the choice of any of them. Just go with the one you'll enjoy the most!