Which kind of Crest Whitestrips should I buy for my first time ever whitening my teeth?

I'm 18 and I've never had the need to whiten my teeth before but recently noticed they were looking a little dull (probably from drinking more coffee and sweet tea within the last year or two) and I decided to go buy some Crest Whitestrips. When I got to the store though, to my amazement there were quite a few different kinds, so I came home and went to the Crest Whitestrips website to figure out which one I needed to buy for my first time whitening. The site doesn't tell me that though! So please help! Here's the link to the site: http://www.whitestrips.com/
--------------------
The classic work great, they just take longer to work (and taste bad when you take them out). They also cost less, which is a plus. I would recommend switching to a toothpaste for sensitive teeth while you are using the whitening strips. I whitened my teeth and it was painful just to drink water from a drinking fountain because they were so sensitive! (Sensitivity happens with all teeth whitening, and tends to be worse with the faster acting formulas because they are stronger). Sensodyne worked well for me. Also make sure not to leave them on longer then stated - I made the terrible mistake of sleeping in the strips one night - I couldn't use them again for at least a week because my teeth were in so much pain! Hope that helps!
Source