An opinionated guide to which AI to use to do stuff

Every few months, I write a guide for people who want to use AI to do stuff. This time, a lot has changed, in part because what it means to “use AI to do stuff” encompasses so much more “stuff” than it used to. Until recently, using AI meant talking to a model through a chatbot in a constant back-and-forth conversation. Now, it means using an agentic system, where the AI is capable of doing the equivalent of many hours of real human work in one go by combining the brains of an AI model with a set of tools that let it plan and act for you. Basically, an agentic system gives an AI a computer to use.If you haven’t used an AI in the last few months, you might be surprised about how much has changed as a result of smarter models and better agentic systems. As a fun example, When GPT-5 came out, I created a brutalist city building game as a demo (you can still play the original version) with the prompt “make a procedural brutalist building creator where i can drag and edit buildings in cool ways, they should look like actual buildings,” and some suggestions for improvement. Less than a year later, I used GPT-5.6 Sol in Codex to do the same thing: you can play it here. If you don’t want to play it, the video shows the difference — it is quite stark!So how do you take advantage of this power? My advice really has two parts. If you just want a chatbot that can give you a recipe, answer a low-stakes question, or help you write a letter, there are now tons of options that are good enough, including the default free models. They are all at least fine when the stakes are low, so pick the one you like. But there is an important caveat: if you are chatting about high-stakes issues, like getting a second opinion on a medical or legal concern, you will want the results to be better than “good enough” advice. For these issues, you will want to use the most advanced models you can get access to, which is either Claude's most powerful models, Opus and Fable, or ChatGPT's GPT-5.6 Sol, set to at least the “High” thinking levels. That is because these models have lower error rates and score much higher on ability tests in complex fields, but they will also cost you some money.You need to pick both an AI model and its thinking level. This chart is a guide to which to select.But what if you want to do real work? There are only two choices for most people who want to get the most out of AI right now: ChatGPT or Claude (I will get to Google later). You can go in other directions and save money, but it will take expertise and know-how, while, starting at $20/month1, Claude and ChatGPT are easy and powerful (but also badly documented and confusingly named). Essentially they give a really good AI access to a computer, and that lets it do real work for you. Giving your AI a computerThere are basically two ways to give Claude or ChatGPT a computer: the AI company can provide a virtual computer for its agent to use, or you can give the AI access to your own. Let’s start with the easier (and less powerful) case. To use the computers provided by the AI companies, the mode you want is called ChatGPT Work in ChatGPT, and Cowork in Claude (the naming will not get less confusing, I am sorry to say). In this mode, you next pick the model and its thinking level — I would start with Sol set to High for ChatGPT, and Fable or Opus set to High for Claude. You can also pick what applications you want the AI to connect to, which lets the AI act on your stuff. Personally, I have the systems connected to my email, a non-private part of my Google Drive, and lots of other applications, but you have to decide what you are comfortable with.Once you are set up, you can do pretty powerful things. For example, I told both systems: “connect to my Gmail and help me prep for the MBA seminar I am giving on Monday the 21st, including building some presentation and demos as inspiration. Answer