It's always best to go with a bigger and known company if you want such a large volume. Something to ask them is how much un-used capacity they currently have. You'll be able to tell if they oversell themselves or not so at peak use things won't get slow.
And of course, you should always check out all of your options - check National-Net who's in my signature. Their response time for completing technical orders for me is around 6 minutes.
Cheers,
Matt