Currently 17BTC worth 19108EUR according to
https://bitcoinwisdom.comOn the same minute, on Blockchain Wallet, it says that the 17BTC worth 17493EUR
What might be wrong?
Well you can't expect blockchain.info to provide perfect updated prices every single minute.
They are after all only a wallet service, they can operate without a price estimate on user balances at all, but they have and that is only an estimate of your total bitcoin value in all of your bitcoin addreses in your wallet.
Even bitcoinwisdom isn't 100% accurate, because you are probably not going to get an account to trade with on a big exchange when you've only got say 0.1 BTC to sell.
Go to localbitcoins and browse the rates of the payment method you want to sell for. That's the most accurate.