We choose "we".

Even if you're the sole author of the app/site, the voice of any text should be abstracted away from your identity at least to this small degree. Use "I" only in testimonials, quotes, or in a "message from our founder".

This discipline helps keeps the voice/tone of the text consistent throughout the app, which inspires trust and confidence. It's more polished and professional, especially if you ever contemplate expanding your team.