Twilio's new international SMS is roughly comparable with Nexmo's. Nexmo's is slightly cheaper in our comparisons. Twilio's docs/dashboard/etc. are far better. (I used to work at Twilio and am a happy customer of theirs at IFTTT)

Not a fan of Nexmo. Pricing is higher than Twilio, deliverability is noticeably worse, and their service uptime is pretty rough.