What Should I Look for in a Reliable Reseller Web Hosting Provider?

I'm planning to start a reseller web hosting business and I'm researching different hosting providers. There are so many options available that it's difficult to know which features really matter.

What should I prioritize when choosing a reseller hosting plan? I'm particularly interested in reliability, uptime, white-label branding, WHM/cPanel access, security, backups, customer support, and scalability as my client base grows.

Are there any providers you've had consistently good experiences with, or features you wish you had considered before getting started? I'd appreciate hearing about your real-world experiences and recommendations.