Is bitcoin more safe than other coins? If transaction minimum fees are small, it could mean that the currency is more risky?
There are many kinds of risk regarding bitcoin and altcoins.
https://en.bitcoin.it/wiki/Weaknesses.
If you are talking about 51% attack, what matter are the total network hashrate and its distribution.
On the other hand, a lower tx min fee would mean a lower cost for transaction flooding, which may prevent other transaction from getting included in a block.