Having used the API a bunch, the ChatGPT API (GPT-3.5-Turbo) feels like it has a 10-second attention span in comparison to GPT-4. GPT-4 is waaaay more powerful for actually building stuff on top of, adheres to your prompt in a much more stable way, and its reasoning is way less unstable in general as well. Writing long blocks of code without making "stupid" mistakes works much much better, etc.
The only downside is: it's so, so, soooooo slow in comparison to GPT-3.5-Turbo. You'll literally have to wait 2-3 minutes for the response with larger token amounts.