Depends on how you'll set it up. If you go the "clamshell" approach, and the MBA is closed, then I'd opt for an Apple wireless kb, and a MagicPad. That way you can use gestures.
If not, just use the MBA as your primary, and the 23" as an additional display. Then use the kb/trackpad built in, so you can use gestures, etc.
My 2 cents [well, actually 3...inflation].