Oo, hard choice... I have two bands that I can't choose between as head-liners! :( I'm gonna go with two support acts and joint head-liners as a cop-out :D
Opening Support: Futureheads - They aren't one of my favourite bands, but I've seen them live and they're absolutely amazing. Their songs are performed so well live and they were really a great band to watch!
Second Support: Biffy Clyro - These probably would've been the head-liners for me, but they simply aren't big enough/famous enough for that! They're honestly the best band I've ever seen live, so good that I've seen them a total of 6 times so far with plans to see them again early next year. All their songs are just amazing live and Simon's voice is utterly wonderful.
First Head-liner: Arctic Monkeys! My all-time favourite band, I absolutely love them. I can't think of a single Arctic Monkeys song I don't at least enjoy, and I've listened to countless live shows from them, all of which are amazing. Unfortunately I've never had the opportunity to attend an Arctic Monkeys concert, but from all the videos I've watched they sound great live and I'd absolutely love to see them.
Second Head-liner: Muse! To be expected, honestly. I've seen them live a few times and they were utterly brilliant each time. Matt Bellamy just has some way of getting the crowd going... it's unreal haha. They're such good performers live and their songs are so diverse and yet all so good that one set list isn't enough, so they definitely deserve the spot of main head liners in my opinion. Plus they're the biggest band on my list so I think they'd earn it by default haha. I'd be slightly put off about seeing them based on their newest album and how different it is to their old music, but I expect they'd still be beyond exceptional to see live again.
I made sure to choose bands that were somewhat similar in genre so the concert would flow, but this is probably my ideal line-up. Just hope the crowd isn't as violent as usual at Biffy concerts! It can get painful :(