I had a t-mobile g1 and now am using a t-mobile g2. They were both fine. Since all these things are Android the difference is relatively minor. I like Samsung in general as a brand and have been buying their stuff for over a decade, but my tilt currently is that they've currently become the expensive brand. Like Sony was back in the day when they were on top.
That said i don't really understand the phone market. Except for hated Apple who has a decent product lifecycle and longish term support all these manufacturers just pump out and endless stream of nearly identical phones and then abandon them after a few months anyway. Hopefully now that we're at 2-4 cores and ~1gb of ram things will stabilize some.
On the FB specifically (and i am a strong detractor of FB and haven't used it in over a year)... i similarly don't understand why they're bailing so soon. Give the thing a chance. It's not like it's HURTING people or something. For example, relatively few people actually buy the Nexus phones and tablets from Google, but they're still around and serve their purpose.