Bottom line is that they both have their advantages and disadvantages.

I have a buggy and i seem to like jumping and bashing it about as well as my savage. The savage i mainly use in rougher stuff, and grass where the buggy gets bounced around more, or where the grass slows it down. I like the simplicity of the buggy, the ease of working on it, and the layout of the driveline(which is the same as a truggy). A buggy will take more of a beating than a truggy will though because of the shorter A-Arms and smaller tires.

A buggy will be stronger than a truggy, takes less power to go as fast(and get there quicker), and the clutches will last longer. It just wont handle rough terrain as well, which is why i have my savage, and IMO the savage will handle the rough terrain i run on better than a truggy will, and as it was already mentioned, the clutches last much longer since they have a low 1st gear for hills, and torque down at low speeds. My $12 integy clutch has 3 gallons on it now and is still doing great. A truggy wont be too good at anything under probably 15mph in off road stuff because the clutch wont be "hooked up" yet.

Here is how I would classify the 3:

Monster Truck- Great in medium to tall grass, big jumps, real rough off roading, ruts, and rough hill climbing, along with mud and water if thats your thing
Truggy- Great on medium rough dirt surfaces, not too good for grass, handles jumps well, handles most off road surfaces pretty good as long as it isnt low speed climbing/playing
Buggy- Great on fairly smooth dirt surfaces, not good in grass unless its pretty short, handles jumps well, and any fairly smooth off road surface they are great for. Most durable of the 3

Really, it all depends on where you will be running, and basically which style you prefer. They all have their positives and negatives, so if you can, its best to have a couple of different rides to choose from.

Eric