Which IGP ?

Hi, I would like to know which IGP (EIGRP, OSPF, ISIS) is used at large networks (MCI, Sprint, PSI, UUNET, ANS, etc.) and WHY ? What are the "real world" pros and cons of each IGP ? -- Marcelo Manta SAGA PGP fingerprint = E3 B8 AC AF 24 61 E7 E5 B8 38 01 D1 3C F4 32 5E PS: I will post a summary of the impressions.