There is no “better”, there are only different advantages. The advantages are obvious—13” can show you more, 11” is easier to hold 🤷♂️. Which size is better for you is based solely on your specific situation and preferences, but personally I shift positions a lot while reading for extended periods which means I need to hold my reading device, so lighter the better. But I find it uncomfortable to hold anything bigger/heavier than the iPad Mini for long periods, and even for that I require a Pop Socket.