I have tried scaling but this is a very cumbersome process and in the end the objects are never 100% aligned at the top and bottom. So how to align those two objects at the same top and bottom position ?
You can use snapping options to do that.
- Set snapping on and choose the closest to vertex option (under the green arrow bellow)
- Enter edit mode for one of the objects
- Select all the vertices
- Then point your mouse to the bottom of the second object and grab G
- Now position the 3D cursor to the bottom : select one of the bottom vertices, then Shift + S and cursor to selected
- Back to object mode
- Set the pivot to 3D cursor
- Then scale S and point to the top of the second object