In the UK, the wedge Amigas are the most common by a large margin. A500/A500+/A600/A1200. I think the A500 is the most common of the bunch and the Plus is probably the least common, due to its battery-related fail.
After that, the A2000 is probably the commonest big-box Amiga, followed by the A4000. Then finally the A1000s and A3000s, which are both reasonably uncommon over here.
The tower models are both rare, but A4000Ts are far more common than A3000Ts. CDTVs are probably less-common than the A4000 but more than the A1k/A3k. CD32s are probably up with the 'wedge' Amigas, they're not too hard to track down.
After that, the A2000 is probably the commonest big-box Amiga, followed by the A4000. Then finally the A1000s and A3000s, which are both reasonably uncommon over here.
The tower models are both rare, but A4000Ts are far more common than A3000Ts. CDTVs are probably less-common than the A4000 but more than the A1k/A3k. CD32s are probably up with the 'wedge' Amigas, they're not too hard to track down.