Since I love low and slow, I'll jump in here. All suggestions so far are good. However, I find myself investigating Orbxs' demo of Tasmania while sitting in the old LIC 7ac Champ a real hoot. It might be that much of my real life flying was in the champ, but it helps that as a flightsim model, it is almost perfect. Very realistic, great visibility from front seat and works very well in FSX. If speed is an issue, I usually end up flying Lionheart's Tailwind. I can be a fairly nice stol aircraft once you master landing with full flaps. The Pacer/tripacer is a wonderful model also, but visibility from VC keeps me from enjoying it as much when trying to get into smaller strips. Ant's Tiger Moth is also wonderful for low and slow, but landing can be a challenge, just doesn't want to slow down. For true stol use, I like RealAir's Scout and Flight Replica's Super Cub. I use the standard 150 and the 95 hp version. The 95 will test your skills getting it to slow down enough to land in a small strip, almost as much as Ant's Tiger.
Just my thoughts. No matter what you try, it is much fun trying to pick the "right" aircraft.