When lifting is worth evaluating
If an existing slab is sufficiently sound and its main problem is settlement, a contractor may be able to improve its elevation and support without removing it. The amount of lift and finished alignment still need to be assessed.
When replacement may be more suitable
Extensive fractures, severe deterioration, an unsuitable slab configuration or the need to rebuild the base may make replacement the more appropriate scope. A new pour can also allow a different layout where that is needed.
Consider the underlying cause
If water continues to wash away soil, simply changing the slab elevation may not address the source of movement. Ask whether drainage or other site work is needed in either scenario.
Compare the complete proposals
Request clarity about demolition, disposal, base preparation, injection work, joint treatment, drainage and the finished surface. Two estimates may not cover the same tasks even when both promise to address an uneven area.
Avoid a one-size-fits-all answer
A contractor should inspect the concrete and explain why the proposed approach suits the particular slab. This website cannot determine structural suitability or prescribe a repair from a written description alone.