If you're a solo developer focused heavily on code, particularly using AI for assistance, Cursor is the way to go. Its advanced AI code completion and ability to manage multi-file edits makes it suitable for creating complex projects efficiently. However, if you need complete openness in your tools, or if your AI use will be minimal, you should avoid it.
On the other hand, if your priority is deploying latency-sensitive applications and you're comfortable handling some operational tasks, Fly.io is the better choice. It excels in providing low-latency server locations and cost-efficient scaling. Just keep in mind that its usage-based pricing could lead to unexpected bills, so if you prefer a predictable billing structure and minimal ops overhead, you might want to steer clear of this option.