Really should be in OffTopic, but Mac is the safest to use with BTC applications on it. I use linux sometimes though.
What makes you think Mac is the safest? It has viruses just like any other OS. But it's proprietary, like Windows, so I'd say it's less secure than Linux still.
The reason many people think "macs dont get viruses" is because the market share is much lower. If your gonna try and scam someone why email a single person when you can email 10 people. Its less secure than linux but I think the system itself is pretty safe.