I'm using HDD on USB, and sometimes aspecially when I'm recording HD channels observe freezing frames. I'm wondering do on e-sata could be better. In box where a have placed my HDD has USB & E-SATA connectors, but my HDD do not work via E-SATA with 900HD. Probably because it is WD Caviar. I even read on other bord about problems with WD's in 900HD. I checked both my HDDs, both are WD's brand and no one work via E-SATA with 900HD. So if U have WD's HDD then forget about E-SATA connection.
every kind of SATA is faster then USB. In my case WD's HDD is not working with ip-box via SATA. So I had only possibility to start it via USB 'til I buy new Hard Disk. Probably Seagete should work via E-SATA, but who knows.