The short answer
ChatGPT is still the best free all-round starting point. Perplexity is the strongest free research tool. Gemini is worth testing if you already use Google heavily. Most people should start with one of those before thinking about paid tools at all.
Who should use what?
ChatGPT
Best if you want one free assistant for writing, planning, and everyday tasks.
Perplexity
Best if you care about sources, search, and current information.
Gemini
Best if your workflow already lives in Docs, Drive, and Gmail.
Claude
Best if you want to compare writing quality before deciding whether a paid upgrade is justified.
When free is enough
Free is enough when AI is still occasional, exploratory, or tied to lightweight tasks. If you are using AI a few times a week for explanations, summaries, brainstorming, or light research, you probably do not need to pay yet.
When free stops being enough
Free stops being enough when limits regularly interrupt useful work, when output quality becomes important enough to matter commercially, or when one tool clearly becomes part of your daily workflow. That is the point where payment starts to make sense.