CEO of communications company here. We send/receive millions of messages with Twilio. It is our go to solution because it is the most reliable in our experience. Plivo is their most direct rival in my view. We've considered them but again Twilio is reliable so we are sticking with it for now but remain open minded.

FYI Short codes don't interchange well internationally. Also sending MMS has all kinds of challenges/limitations. If I can be helpful at all I'm... dave @ sendsmart.com.

Cheers