Fees and Transaction speed definitely - with new upgrades coming out in the next year (EIP4844) L2s can handle thousands of transactions per second.
The UI is really up to the apps, the good thing is there are many teams working on payments so there will be plenty to choose from to find the UI you like, and people will be able to pay via the same wallet. Stripe already has USDC payments on crypto rails and Visa is working with Starknet to integrate with these L2s too.
All the L2s with their usage, security, speed and tradeoffs are at http://l2beat.com
The UI is really up to the apps, the good thing is there are many teams working on payments so there will be plenty to choose from to find the UI you like, and people will be able to pay via the same wallet. Stripe already has USDC payments on crypto rails and Visa is working with Starknet to integrate with these L2s too.
All the L2s with their usage, security, speed and tradeoffs are at http://l2beat.com