When it comes to rendering I prefer the Mitchell-Netravali Anti aliasing filter, for the Indirect illumination. I have used Irradiance map for primary bounces and Quasi-Monte carlo for the secondary bounces with the irradiance map preset to High with 70 in HSph. subdivs and 40 in Interp.
Samples. GI Enviroment (skilight) Override MAX's turned on and here's the MAX fresh render :
I used Photoshop to Paint the Flame by making a selection with the pen tool then applied some
Feather and paint bucket it with a suitable colour and finally started erasing with low opacity eraser the lower part of the flame (cause that's how it should be); with some color and contrast adjustments I finalized the image.
I hope you like the image at first place and I wish this little tutorial gave you some ideas