Kind of depends on the situation. If your child is home because of some illness then inhome care trumps a daycare center. But there is the issue of the comfort level.
We have used an agency for backup care and it has worked well - and when we've known in advance that we'd be needing it we were able to learn about the nanny they would be sending, and even sometimes talk to her by phone before she came. That helped a great deal.
But in your situation I think the Bright Horizons option works perfectly well also (especially if it's in a setting where one of you can visit during the day).
Good luck.
