whats the best simulator for circuit uisng Arduino?

HI i am doing a project using Arduino board. so i want to first simulate my circuit so can you suggest be some best simulation softwares. thank you 8)

http://123d.circuits.io/...is a free online circuit simulation platform that supports Arduino.

Any downloadable freeware ones you can own or others you don't pay through the nose for?

Proteus.

Will any of the above simulate the arduino?

LTSpice is free, and a very useful tool to learn how to use if you are willing. Though how you add in the Arduino, I have no clue. Its just good for figuring out what analog circuits will do. Of course you have to find or build models of various parts, but Linear Technologies has a lot of those.