I think reliability is the #1 feature at any stage because if you're unavailable, you're at best useless and more than likely you are actively harmful because your users have an expectation.

However, if you're unavailable outside of times customers don't expect you to be there then you're not actually unavailable. This is more likely for an early stage start-up, but you don't typically choose or know when you're expected to be available nor do you always get to choose when you're unavailable.