I personally very much prefer the Two Little Fishies Phosban 150 reactors over the BRS reactors. The BRS reactors are pretty much RODI holders, and it can be quite inconvenient to unscrew the whole canister to change the media.
But either choice will work, and both choices are very popular. If you don't have a sump and will be placing it on the back of the tank, you pretty much will have to use the TLF model unless you're willing to mount the BRS reactors to the wall behind the tank. If you have a sump, either choice will work well.
You will require a pump to feed tank water to the reactors. Potentially, you can run it off of your main return pump. That's less than ideal, though, as you have to shut down your main return pump to service the reactors, or place shutoff valves between the return pump and the reactor. A better choice is the Sicce Synchra Silent 0.5 pump dedicated to feeding your reactor - they're about $40.
For media, I'd highly recommend the Bulk Reef Supply High Capacity GFO. The particles are considerably harder than many other brands of GFO out there and so you don't run the risk of pulverizing the media and distributing it in your tank.
You will also require a good phosphate test. The best are the Hanna Checkers. The 713 is a good one for higher ranges of phosphate, while the 736 Ultra low range checker is useful if you wish to keep a very low phosphate level.
Whatever you choose, go slow with GFO if you have corals in the tank. Corals that have become used to high phosphate levels can wither and bleach if the phosphate level in the tank is suddenly dropped to near zero.
