I am looking for web wallet for ethereum such as blockchain.info with API to send / generating new addresses / receiving Ethereum,
what is trustworthy?
You can use both MEW and MIST.
Download MetaMask/Mist and add it as extension to your browser. Make an account and sync it to MEW (MyEtherWallet). You can use your Mist account for sending and receiving Ethereum and MEW for converting ETH to BTC.