I think twitter is one of the most promising "social media" (are we still calling it that?) stocks out there. Where Facebook's main audience (teenagers) is jumping ship, I think Twitter has too many of celebrities and famous people "locked-in" to their platform for a comparable exodus to take place.
Added to that, media like Television have been integrating Twitter into their systems ( live tweeting, tweet voting etc. ).
Twitter, just like Facebook, is grossly overpriced/overvalued. The number of users for both are impressive to say the least, but neither is making a profit that can justify the value of the companies. Both companies seem to have a business plan straight out of the dotcom era, that is: "let's slap some ads on and see if that works".
At this point I think we have seem what will be the downfall of Facebook, teenagers not thinking it's cool. As for Twitter, it might be a US vs. Europe thing, but I honestly don't know more that a handful of people using Twitter and all of them still have Facebook as well. Twitter is a broadcast platform nothing more. That works great if you want to follow celebrities, but if the celebrities are the reason for using Twitter for many, then Twitter is going to be much more vulnerable to an exodus that Facebook. Facebook users won't move to a new platform before all their friends have moved as well. With Twitter you just need to move the top celebrities and their followers will leave as quickly as they signed up.
In my mind Twitter has an impressive broadcast platform, but they aren't making the money to justify the value of the company and have no clear way to do so in the future. Someone is going to have to foot the bill at some point. No one is going to pay a subscription fee for neither Twitter, nor Facebook. That leaves ads or having companies and celebrities paying for their posts.
Twitter has a funny way of working like an little bubble. People on Twitter believe that everything revolves around Twitter, while the rest of the world are at most vaguely aware that it exists.
I would like to respond to your insightful comment about celeberties moving over to another platform.
I think this is just not going to happen very soon. I would like to compare a twitter account a lot more to a e-mail address. Celeberties and brands ( lets not forgot about brands ) have worked very hard (or waited rather long, at least) to get their millions of followers and their @username signature.
I think this is what causes a kind of lock-in: moving away would mean that your messages would get a lot less attention and having to wait a long time to be back at a million followers AND abandoning your @username, which many people have come to know you by.
Now I don't know anybody by their Facebook profile URL, while I know many celebrity @usernames, even though I don't use Twitter. Finding somebody on Facebook is the same as finding anybody on any profile site. You have to use the search, there is no added value. Twitter has a very strong weapon here with their @username offering.
Also, I don't think a new platform could offer enough extra's for them to take the step. Another platform would have to offer something so special that it justifies leaving a million followers behind. I don't see this happening because the strength of Twitter is its LACK of features. You type something and move on. You see how that cancels out any newcomer?
I'm from Europe, and I see a lot of people using Twitter. If I look at my Facebook stream, a lot of the status-updates are coming in through Twitter, or at least apps that post to multiple networks.
Also, I think that I should add that both you and me are commenting from own experience, neither of us is saying anything based on market research. So let's not keep doing this :)
I think if you just look at the shear number of followers mainstream (i.e. CNN) and alt (Vice) news accounts have or the same for financial news accounts, it becomes pretty obvious that a huge number of Twitter users rely on it for REALLY important information. I don't look at customized Feedly or Flipboard type aggregators anymore, and why would I? The information I get from who I follow on Twitter is available sooner, is summarized and usually has the option to dive deeper. While we can see that celebrities have huge follower counts, because their accounts are often water down by third parties, it seems logical that people follow them as a way to just say they 'like' them and not as a source of important information.
Added to that, media like Television have been integrating Twitter into their systems ( live tweeting, tweet voting etc. ).
Looks promising enough to me.