As a serious poster, I would like to say that if you don't mind slice-of-life anime and otaku references, then you should watch Lucky Star.
Also, if you are a guy, I believe you should watch TTGL at least once in your life.
One more thing, if you're going to watch BOTH, then make sure to watch Lucky Star first, THEN TTGL. You will understand after you watch it.
One final thing:
For subs, go with [Black-Order] for TTGL up to episode 19 (that's all they did), and then look on Tokyotosho for subs by [BSS] for the rest. I can guarantee that you will never regret watching TTGL.
Also, the moment you read this, close the window because there will most likely be spoilers that will ruin the epic nature of TTGL.