Despite this being one of those pointlessly revived threads, I'll jump in...

Worst:
- Sheraton Barra, Rio de Janeiro
- Sheraton Philadelphia (pre-reno)
- Sheraton Great Wall Beijing (closing)
- Sheraton Santa Maria de El Paular (closed)

Best:
- Sheraton Edinburgh (now Sheraton Grand)
- Sheraton Hiroshima (now Sheraton Grand)
- Sheraton Lisbon
- Sheraton Porto
- Sheraton Reserva do Paiva, Recife, Brazil