You are a student or lack of money
one lens only: 24-105 mm for every thing
You have some money:
1. 24-70 mm
2. 70-200 mm
3. 150-600 mm
You are not short of money
1. 15-36 mm
2. 24-70 mm
3. 70-200 mm
4. 100-400 mm with canon or 200-500 mm with Nikon
5. 600 mm and 800 mm
6. 12 mm wide angle and 100 mm macro
If you are a professional:
fixed zoom