which virtual server will be hit?

For normal return traffic, you would not usually need a second forwarding virtual server.

Once the initial flow hits internet-vs, BIG-IP creates a connection table entry for that session and keeps the flow state (including things like the return path / last hop information). So if the original flow is something like:

192.12.0.1:10729 -> 1.1.1.1:80

the return traffic:

1.1.1.1:80 -> 192.12.0.1:10729

would normally be matched against the existing connection entry and forwarded as part of the same flow, rather than hitting a different forwarding VS.

I’d only expect another forwarding VS to matter if this is actually a new connection, or if the return traffic does not match the existing flow tuple/state.