We have always used apache as a reverse proxy and it has never been a problem from a performance point of view, performance issues has always been related to the database, business logic, network, disks and so on.

Using nginx might enhance a bit performance, but compared to other modules of the overall environment such performance gains are neglectable and unnoticeable for a normal user.

In our latest product I wanted to switch to nginx but I was surprised that for windows it is only in BETA version, and since our application MUST be deployable to both Windows and Linux environments we preferred a consistent software stack hence we stick on Apache.

The plan is to reconsider nginx once it officially supports windows, since no serious customer would accept a beta version for a production environment.