Why should it be easy? Not possible to specify unless you say what your backtest should consist of. Excel is free form enough for alot, but too functional for more flexible rules. My current choice is ruby because very little overhead on syntax/semantic rules, types and unnecessary dependencies in code. However not fastest running, need to avoid speed bottlenecks (ie. bad use of cs algos) and be a good/experienced coder.
If you dont want/can make your own backtest, how do you know what youre doing?
Now, best way is probably right in front of your nose, what best suits you now. Can always move on later after having learnt what you can learn. Its a fallacy thinking you should be stuck with your first prototype, but oh so tempting.