Comment by duskwuff
Telegram's bot API is a lot easier to get started with for sure. It's got some rough edges once you start trying to do anything more complex, though, and the underlying MTProto API is nothing short of bizarre.
I'd urge caution before using them as a component of your business, though. Their business strategy is pretty chaotic and has relied heavily on weird cryptocurrency-adjacent plays (e.g. TON / Fragment / gifts). They've made a couple of attempts to introduce business features, but I'm not sure they've had any substantial uptake.
Yeah, which is ironic given that it is not E2EE (unless specifically opted in for a private chat, and even then some would argue the MTProto crypto isn't good enough, although those people wouldn't trust WhatsApp ether). WhatsApp is overwhelming associated with legitimate (though in many countries, primarily overseas) users, and Telegram is somewhat associated with shady activities.
That said, Telegram is likely a lot more open for a business type that is legal but still regulated or illegal in some countries (legalized/unregulated substances, tobacco/e-cigarettes, adult content, etc.), probably less worried of random bans/demonetization.
Despite not being E2EE, Telegram also seems to have higher usage in censored countries (Russia and Iran etc). Once a Russian guy in Korea randomly asked if I had Telegram wanting me to take a picture for him since his phone was dead -- obviously had no idea that sounded like a massive scam flag to most Western users.