There is no best stack, only a best fit
The right stack depends on who builds and maintains it, what the product must do and what you are optimising for. A marketing site the content team edits every day needs something different from a real-time dashboard.
Popular, well-documented tools usually win. They are easier to hire for, have answers to common problems and keep working for years.
Next.js, WordPress or headless?
Next.js suits products and sites where speed, custom interfaces and developer control matter. WordPress suits content-heavy sites that non-developers edit every day.
A headless setup uses WordPress or another CMS for editing and Next.js for the front end. You get both strengths, at the cost of more moving parts to host and maintain.
Common mistakes to avoid
Picking a stack because it is new, splitting into microservices before you have users, and choosing tools nobody on the team knows. Start simple; you can scale the parts that need it later.