I use coinbase and Gemini for depositing cash from U.S. bank. These two are good for U.S. residents and bank ACH or wire are fast and fees are cheap.
Coinbase has GDAX , which allows cheap trading with same login/password.
give me numbers please , what interest per 100$ etc
Actually you can do almost zero fees. For example, I found a crypto-friendly U.S. bank called Ally bank, an online bank with no minimum deposit requirement.
With Ally Bank, try sign up with Coinbase/Gemini and use ACH only (electronic transfer among banks), you got no fees deposit into Coinbase/gemini. At Coinbase, then you GDAX to buy and sell bitcoin/litecoin/bitcoin cash/ether at very low fees. Gemini fees is slightly higher.
ACH works better for small amount on both Gemini or Coinbase/GDAX for no fees. But the speed of transfer is slow, several days. Wire is better and faster, but wire usually cost wire fees, a bit more. I think wire fees from Ally Bank to Gemini/coinbase could cost $20 USD.