I just checked their website and they sell "kits" (tent plus LED panel), so I chose the 4'x4' size and looked at the choices. They show a
Mars pro II 1600w Epistar 320 and a
Mars Pro II 1200w Cree 256 option as the top two choices for that size tent kit, so you could probably consider those your two best choices if you wish to use only one LED panel to cover the tent. Neither product is particularly
cheap, but they are both pretty powerful lights and, by their specifications, either should perform great for you. If you plan on growing autoflowering plants in your tent, you should have no problems supporting a "standing room only" (lol) grow.
The Cree model appears to be a little more efficient, a little more powerful, and a little less expensive to run than the Epistar model - but the Epistar model is, I believe, $153 cheaper.
Another option would be to purchase multiple "smaller" LED panels. This would have the benefit of allowing you to position them at different heights - which could be beneficial if you are growing more than one strain at a time and are either unable or unwilling to train all of your plants to be the same height. It might also allow you to reduce shadowed areas and to get some additional benefit from the "third-light effect." I don't know if going with multiple, less powerful LED panels would work out to be more or less expensive than purchasing one powerhouse.
All of the above is strictly my
opinion. I'll "shut up" now and see what Sara recommends.