The rate at which ethereum is developing is intense no doubt. They have huge corporations in the Ethereum alliance backing them, a great dev team, and they are gaining more public attention as every second passes. Growth however is a double edged sword. New glitches are constantly being found in the platform and with more money on the line, malicious users have a greater incentive to take it down. Bitcoin has been through hell and back and is still standing plus ready for whatever will come its way. Ethereum on the other hand has not been through years of intense scrutiny and is therefore riskier. The next DAO could be right around the corner. I remember reading the other day on certain wallets users found a glitch where if they shifted and right clicked they could multiply the amount of ether in their wallet by 256. It has been fixed since then but to summarize ETH still needs to prove itself.