I will go for the safest... Properly decentralized exchanges are safest for me. I can't imagine leaving lots of coins on centralized exchanges long-term. Lots of bad thing could happen to it. But with a fully decentralized exchange, you control your keys... you can hide your keys and take your minds off your coins as long as you want-- peace of mind.
By the way, the centralized exchanges can change their policies anytime and that could affect your ability to access your funds or use them easily. Decentralized exchanges are great.