Heh... I just loaded the assault rifle up with grenades, and chucked one through the door the moment the MiB's blew it in. Cleared the corridor in one shot.
I always fought the MiBs in that bit (but tranqilised the UNATCO guys) but once the hotel was cleared, I always just went out the window in the apartment, rather than the front door. More stealthy that way. Unfortunately, also a brother-killing action.
I've never failed to save Tiffany Savage, though. I am a stealth sniper ninja dude in that gas station. Master rank in sniper rifle, with a silencer, a laser dot, maxed out accuracy mods, plus the eye augmentation that increases accuracy, and I breezed through that section. Headshotted everything except Tiffany's guards, who I gas grenaded and then shot with my stealth pistol.