I've flown a number of different aircraft whilst performing fire spotting duties. 150 (I'm not kidding, we were forced to during the fuel contamination debacle), 172, R172K, 182, R182, 206, 210, PA24-260, PA28-160, PA28-180, PA32R-301, PA31-350, PA34, PA38 (dreadful), C33, V35A, A36 and some others that I can't remember.
A lot of the firespotting I've had to do was in the A36. Some air observers/air attack supervisors had issues with the wing being on the 'bottom'and obstructing their view of things. In reality it was never a problem. If you're going around in circles over a fire in a 182 for example, you constantly have to lift the wing to keep the fire in sight. That doesn't happen in the A36. And when you sit there and actually take note of how much ground the wing hides, it's not a lot. If you lean forward slightly you can see straight down past the leading edge of the wing.
The 172 is OK if your just keeping station over a fire, but if you're constantly having big changes in altitude where you might be checking some aspect of the fire and then climbing back up to altitude where things are a bit cooler and a bit smoother, they're a dead loss. You only just get back up there and then down you go again. There's also an issue with the amount of power you have on tap and hence the aircraft's performance (or lack of it). I've only been caught out twice at a fire over the years and one of those incidents was in the 172 and it was due mainly to only having 160 horses to play with. It nearly just wasn't enough.
A coulpe of the poster's above mentioned loiter time/endurance. I won't spend any longer than fours hours max over a fire. It can be hard work out there some days and after that period of time you can start to feel rather fatigued. Both crew members by then are pretty keen to get back on the ground and have a rest. If the aircraft has a six hour endurance, we don't tell anyone!
Personally, it's never worried me in the slightest about operating a single over a fire. If the engine is going to throw a wobbly the aircraft would be put down in the black stuff. It's not going to burn again (the terrain that is). Having said that, a twin might be nice if you're operating up in the high country. But over the hundreds of square miles of flat mallee scrub, for me at least, it's never been something to worry about.
If you fly a recce of the local fire district and do 'one with the lot' it's a distance of just a bit over 500NM. That's around 3 hours in a R182/210/A36 or 5 hours in the 172. The 210 or the A36 might be the way to go. But the real question is, which one of those makes more dollars for you?
But to answer Flog's question, it'd be either the 182RG the 210 or the A36. They've all got enough power to keep you out of trouble. They all carry a good load. They're all reasonably fast. And if you have to sit over a fire for awhile, you can wind all three back to 80 kts without any bother.
But for me it would be the 210 (as much as I love the fabulous A36). It's got two more seats way down the back than the 182RG, if you have to take a crew somewhere. You also get to sit in the shade. The A36 can be hot inside the cabin on a hot day. And let's be honest, only girls fly their A36's with curtains on the insides of the windows!
There you go. A36 on fire spotting/air attack duties.