Last week wrote about how BTC solves the double spending problem. This was prescient because this week there have been two high profile attacks on smaller chains. Both BTG and Verge have been attacked and some exchanges have lost money due to double spending. No ordinary users are known to have been affected.
The moral of this story is for maximum security stick to the biggest coins with the best understood protocols and the most hashing power. Bitcoin is clearly the most secure coin by far.