I have flown the C-182, ACA Scout and PN-68 on aerial spotting and firespotting/air attack sorties. IMHO the Scout was by far the best for low-level stuff. Good power to weight and endurance, fast (?) enough for the area covered while capable of very slow speeds when required to loiter. It's also able to land just about anywhere and is very, very cheap.
That said, It did get very crowded at LL over a fire sometimes, particularly when trying to work under a step in suburban interface areas. You'd often have orbiting and/or streams of fixed wing bombers, helitaks and firebirds, bird dogs and news helicopters all sharing the same patch of sky with minimal, visual separation. I think it's time we moved beyond that and into high-level detection and attack supervision platforms. Aircraft fitted with EO sensors and voice/data link back to a command centre. That way fire commanders can be kept entirely in the loop, in real time, with a minimum risk to combat agency personnel.
The DA-40 can do it, but it's endurance is not great once you put some payload aboard and it's not the most reliable machine. I know someone had a BN-2T Islander fully equipped but I'm not sure if thats still running. Maybe a PC-12, 'van or PAC-750 if you can go SE?