Graphics card shopping. Recommendations?

Hi,

I am looking to purchase a graphics card for a museum installation that will be running a unity program. We have some fairly complex elements in the scene so a beefy graphics card is in order, (it runs best in our newest mac laptop). The installation machine will be running windows. I would like to know what features I should look for in a graphics card. Nvidia or AMD? Does cuda cores or stream processors make a difference for Unity? Is memory or clock speed more important? Does anyone have a specific card to recommend? It will be running in a museum all day without shutdown so cooling and reliability as well as power is also very important.

Thanks,

-Matt