I have a bit of a messy setup due to availability issues and price fluctuations with the recent shortages. Currently, I'm using one LG UltraFine 4k display at 27" - it's beautiful, text looks super crisp and it works perfectly fine out of the box with my MBP. For a secondary display I use a 1440p BenQ which has been a source of pain with macOS, because macOS doesn't play well with 1440p displays. To make it work without looking like garbage I use betterdummy [1], but this also has the side effect of requiring a lot more window management that I sort of scripted with hammerspoon.
It's really not a good time to get a monitor for a macbook: the onboard display on the new ones is gorgeous and very little on the market comes close at a reasonable price point. This recent article [2] goes into the dismal state of affairs better than I can put here. If you're just getting into external monitors and have a pretty large budget, I would recommend the LG UltraFine 5k specifically for its ability to have a single cable work for display + power + USB-C hub. I wish I could get one but they're heavily marked up here in India.
1: https://github.com/waydabber/BetterDummy
2: https://www.caseyliss.com/2021/12/7/monitor-liss