There is no such thing as the
best circuit simulator software.
Every software has it's advantages and it's drawbacks. To find the software best suited to your expectations and needs, you will have to define the requirements and/or limits.
An example: A software may be free (good for your purse), but may be limited in features (bad if you need them). Or it may have all the features you want (good for you), but be expensive to buy (bad for your purse).
Personally, I use
LTSPICE IV. This is software of the first kind:
- free
- rather limited library of components
But it has all the typical SPICE features plus a graphical editor and waveform analyzer. Missing models can be integrated manually into the existing LTSPICE IV libraries or you can add you own libraries.