Twilio is the leader. Strong API, excellent documentation and reliable service. I suggest Nexmo since their API has smaller learning curve, offering better prices and also reliable solution. Also Nexmo offers more call per sec. 3 vs 2 and 2, out of the box. Good luck

Twilio documentation is very good and as a platform it just works. It's robust and reliable. We road-tested plivo and it wasn't anywhere near in terms of docs or support. In fact their support was terrible at replying to us. 48 hours to answer basic questions.

That's said, were also using sendgrid by twilio and that's not been pleasant . Their email builder appears to be react based but written by a team who don't understand react very well. That's a nightmare as yet

Twilio might be not cheapest, but they have awesome documentation (a lot of examples), easy to use API and libraries. I think it's a very good product to start. If the bill will become too heavy, you can shop around for economical options.

stackshare doesn't seem to have this in the stack list yet, but in my experience Twillio is attractive. It's good for basics, their acquisition of SendGrid gives them a bit more market share.. They are stronger at marketing to those that benefit them. That said from my understanding SendGrid leases the networks, channels, and lines. While their interface is friendly, their pricing suited for lower volume, you want to look at what they are using via an API, a contract, etc. Is it a more friend UI to a combination of others. What redunancies do to they have, try their support. It's not that Twillio is bad, it's about the volume, the use case, the liabiitlies you might have to your end-users if Twillio isn't the right choice. Another option is Bandwidth. You ask for affordable, Twillio is an option, but front end costs v/s the costs of support you'll need to consider. Bandwidth has more reliability but requires more engineering and more skillset. Another option that is worth considering, not the most affordable, but https://www.zipwhip.com/ have perhaps options that might be higher and the cost is relative. Wight costs, of support costs of integration, cost of scale, costs of a volume..