I have Tweetie, Twitterific Premium and Twittelator (plus Birdcage, for composing Tweets I later want to post). Each of them have their own good points, of course, but I would say definitely go with Tweetie:
It's got a very elegant UI, including all the features like Timeline, it's cheapish at U$2.99, and like Twinkle -- which I haven't tried -- it has the "Nearby" functionality. If you're going to do something, at least give yourself a chance to like it by getting a decent app.
As for whether you should even be on Twitter, that's really your call.
I personally was there when IRC and chatrooms started; I was there when Facebook took off, and when Linkedin made waves, so there was no way I would miss out on Twitter. Instead of making friends, like on Facebook, on Twitter one can actually have a link to and speak to the power brokers of this world, real-time (I'm not kidding. A friend of mine now regularly Tweets with Karl Rove, of all people).
If you just want a time-wasting device, to chat with random people, not all of them worth your time, check out the Distant Shore app. It'll be right up your alley.
But Twitter is just new enough so that it hasn't been ruined, like at times I feel Facebook and certainly Friendster/MySpace have been. Everyone should be on it, if only for the interconnectivity.