<u>Return from the top...</u> If for what ever any reason you end up with a reverse siphone thru a return placed at the bottom you'll lose nearly all water in the tank during a power outage.
That being said... I have one of my tanks designed with a spraybar blowing across the bottom of the tank. You can place the return where ever you feel flow is a requirement. Just make sure that you design it in a way that will be sure to stop a siphon in the case of a return pump failure.
I would think the "shimmering effect" would only apply if the return flow was very, very, low, most return pumps worth their salt would need for the flow to be somewhat submerged.
