My first two 120mm holes I cut didn't go to bad (used a RotoZip--basically a big dremel), but they are rough around the edges. All I did then was take some door trim and wrap it around the edges so it looks a lot better and is safer for the hands
[typical dremel--not mine]

[rotozip--what I used]

The rotozip would be an excellent choice if you get the right bits (same with the dremel really) You can cut some blowholes/windows/and do some pretty wicked designs if you have the patience. We used to have one but I broke it after the first time I used it