You didn't ask the country so my answers might slightly differ

1. India - Kite by Zerodha[0]. Zero brokerage fees (!) for equity delivery. INR 20 for options. Easy to understand UI and great community

2. Australia - Superhero [1]. Zero brokerage for buying ETFs. Easy app but given my infrequent usage (once a month) not really a problem.

[0]https://zerodha.com/ [1]https://app.superhero.com.au/log-in