All else being equal, you could conceivably push a higher data rate on the forward link. The apertures are the same size, just the transmit and receive aperture

All else being equal, you could conceivably push a higher data rate on the forward link. The apertures are the same size, just the transmit and receive apertures are reversed, so geometric losses would be exactly the same. However, you can get a much more powerful laser on the ground since you don't have to worry about the power and thermal constraints you have with the transmitter on the spacecraft. This advantage will be pared down somewhat as the spacecraft won't have as sensitive a detector as the ground station (since it's harder to actively cool it for low dark count, for example). But on balance I expect you will come out ahead. That said, on real world deep space missions, forward links are generally much slower than return links. This is because the slower you go, the better margin you have to close a link in adverse conditions (eg: mis-pointed spacecraft antenna for an RF link). Since you are completely screwed if you can't command the spacecraft, TT&C engineers will always go for a slower rate on the forward link for added Murphy insurance unless there's a pressing need to do otherwise.