Blender.
The only reason I got into 3D is Blender. I wanted to make some models for my favorite game many years ago and the developer of that game used blender to make them. I follwed the famous Donut tutorial (the old 2.7 one) and it opened the eyes for me that blender was so much more than a modeling tool. I had used SFM before in small amounts to make tf2 wallpapers, so I guess I wasn't completely new to CG, but Blender kinda shaped in which direction I steered my life.
