... Use blockchain.info or a better wallet like xapo if you're interested in using online wallets as you can get an idea of what fee you should pay and xapo pays the fee on your behalf which is better.
Actually, I was wrong above... this is the most ridiculous things I have read today... 
For one, Xapo is a terrible service and is not a proper wallet... you have no access to your private keys... Also, if Xapo is paying the fee on your behalf, how can you get any idea of what fee you should pay?
I know that xapo doesn't let users control their private keys and hence even recommended blockchain so that the user gets an idea of what fee should be paid. Xapo paying the fee on the user's behalf makes the transaction get confirmed faster compared to blockchain where sometimes despite of paying the right fee, the transaction takes hours to confirm. Xapoo pays 225-400 sats/byte.