Need advice! Best investment/Savings account with flexible withdraws

Hi everyone, I not to knowledgeable with these things. I've got a family member who has just turned 18 and they want to put the money (around £2000) somewhere that has flexible withdrawals for emergencies but offers the best rates. They have asked me about ETF, the Chase Savings accounts and compounding accounts. If you were 18 and wanted to pop £2000 away where and how would you invest it?

Thank you in advance