I find Twitter MUCH easier to use on desktop. On the phone I look at it for a minute and give up since I can barely tell what it is I'm looking at. I don't see any deficiencies in the desktop Twitter. It's very clear and easy to use and navigate through.
Agreed that Reddit (on desktop, never tried another) is a horribly laid-out, unnavigable, confusing forum. One of the worst layouts I've ever seen. It's extremely hard to simply read one of those celebrity chats from start to finish with every post the celebrity made.