Personally I’m enjoying OpenSCAD… but it’s not a nicely packaged GUI
Blender is nice but I found it has a steep learning curve for some folks… now I have to admit… I used Blender for other design projects, not 3D printing, so others will have better advice on that.
Curious about what bugs you are finding with 123D?
My daughter used MeshMixer in a 3D Printing class she took last year… she liked that one, but I’m not sure if you get a short trial version or if it has a long-term free version.