Different costs for T1, how to choose?

The company I work for just moved to a new location. There is no DSL or cable access available to the Internet.
I have been shopping for T1 access and noticed there are so many differnet prices available. From $495 to $1,599 per month.
My questionis; What should I look for with these service providers?
Is there a service available (website) that rates T1 ISP’s?
Thanks in advance, Rob