I'm not sure if I understand your meaning correctly, but just to clarify, Showtime is an expansion pack of the Sims 3, which means that if you want to play that, you will need to install the Sims 3 base game first before you can play it.
They are not separate games, so in other words, if you don't have the Sims 3 in the first place, you will need to get it in order to play all the other expansion packs.
Edit: Oops, read your older posts and got the impression that I have made a mistaken assumption after all. My apologies.
Regarding your original question, it depends on whether if you want the extra contents that comes with the limited editions, at an extra cost compared to the regular version. As for myself, I bought the Katy Perry version because it was the only version left in the store and I was too antsy and could not wait to get my hands on the newest expansion pack, haha. In my opinion, the bonus contents are nothing to write home about, unless you like to play with all those cutesy fruity themed objects often - but then again, you can also download items like those for free on various Sims 3 sites created by other players.
Anyway, here is a Showtime review for the Katy Perry version for your information:
http://www.youtube.com/watch?v=MjD6MIbmGc8&feature=plcp&context=C4ecb352VDvjVQa1PpcFNFMfFljW3yMhBNvxEYtKpk9X7XA3tD4to%3DHope it helps. =)