I will be the first technical employee of an early-stage startup. I don't have a ton of experience (so something like CTO would look bad and misrepresent me) but I will be doing all the software development at first and leading development when we expand the team. I've been given the freedom to pick my title.
I know that the title doesn't matter a lot, but I still need to pick one. Any advice?
Lead Developer sounds appropriate. Here is an interesting post about this very topic.
This way, you can either grow into the CTO position or into Sr. Developer, depending on your aspirations.
If you read the CTO job requirements, you'll find that many competent developers don't want to follow that path (can't blame them).
In a similar position during the first dotcom boom I picked "Head Techie". It's probably my favourite job title of my career ;-)