In reply to sterobinson: Practically speaking, Meru is a better bet. No extra borders to cross - no extra visa to acquire - less time to travel between the two. It depends on your timetable.
But in fact, if you make the long, slow version of Kili and climb the western breach, you can acclimatise along the way and stop to smell the roses. Great walk in, exhilarating climb to the crater (where we camped!!! and played on the glacier!!). If you do stop in the crater, you can get up at a reasonable hour on summit day and still be there for the dawn - amazing. Take 10 days up and down. What's the rush?
Try this outfit and mention my name if you do.
Dina@mail.klubafriko.com
I'm pretty sure they are still operating, but outfitters come and go.