I have to say both have there perks, but personally after having an aggressive for a year, then switching to a reef, i personally will never go back to aggressive unless its a second tank. My main display will always be a reef. Several reasons : Color, if done correctly they are absolutly jaw dropping; Again remember some people have 2 corals and a clown and think they have a reef; When others will have 30+ corals and 15+ fish. Movement: Reef tanks have so many different forms of life from sps to inverts...crabs/shrimp..etc ..plus small fish, large fish, cleaner fish...etc always something to watch out for.
Aggressive is nice because some of the fish have personality...which is great but again its just them and the tank and a few pounds of rock...which is great ...but other than seeing them swim there isn't anything more to look at...plus you cant have verts.
Perks to aggressive ....it is easy to take care of...some will say its hard...but honestly it is easy.
Some, but not all say reefs are hard to take care of...I honestly dont think they are...mine requires almost no work other than feedings...monthly water change and daily water added. I dont check my levels unless my corals show signs of distress (over time you can tell if something is off...by the smallest things)
again to each there own....but I personally suggest reef.
either way you should be using RO/DI water, good lights..and a UV...
so basicly its just a matter of how much do you want to spend on your water quality.