Would biorevitalization or PRP injections deliver better results for skin laxity in the lower face? 45 y/o female.

1. For injections, I would recommend considering a second generation platelet concentrate, such as platelet rich fibrin (PRF) - specifically, liquid PRF. Some studies have shown a higher increase in growth factor release in PRF versus PRP for a longer time period. PRF is very similar to PRP, there are just some small, but important, modifications to the processing procedure.
2. When you say "laxity", are you actually looking for a lifting effect without surgery? If you are, depending on the area of the face, doing a thread lift may offer better results. It also depends on what specifically you are trying to address.
Ultimately, PRP injections with PRP microneedling is going to offer better results than either procedure alone. Also, rather than doing them months apart, you may want to consider doing a set of monthly treatments for 3 or 4 months.