SR1, easily.
I didn't have to go through a loading screen every time I wanted to do something. It was sleek and small, and whilst I don't mind the larger version, it just went a bit over the top.
I want to talk to all my crew members on the SR1 for whatever reason: I talk to all on the first leader, I take a 1 second elevator ride down and talk to everyone on the second level.
I want to talk to all my crew members on the SR2 [Cerberus] for whatever reason: I talk to the guys in the CIC, go through a 1 second loading screen [I wish there wasn't the fade in/fade out. That takes more time than the loading on my PC], talk to the guys in the living area, go through a 1 second loading screen, talk to the guys in the basement. In addition, everyone on the SR2 is further away from each other, so I've got to run around the ship for ages just to talk to people, whereas in ME1 it was relatively easy.
The SR2 - Alliance... No. That was stupid. Half the ship was blocked off, yet it somehow had more loading screens. Fewer areas, more time spent loading. If I wanted to talk to everyone in my ship I'd talk to the people in the CIC, go through a 2-3 second walk through a scanner, talk to everyone in the war room, go through a 2-3 second scanner, go through a 1 second elevator ride, talk to everyone on the next level, go through a 1 second loading screen, talk to everyone in the basement. That damn scanner was the worst idea ever, seriously.
I also preferred the greater immersion that 1 provided. You actually rode the elevator up and down, and you stood in the decontamination area whilst it loaded, rather than idly staring at a loading screen. Far better IMO.