I'm also looking into getting my first Chanel and I'm currently deciding between the GST, Jumbo or Reissue 226/227. I really love the Jumbo and Reissue but it's so darn expensive...the GST is so cute and goes with both casual and dressy outfits....I might get the GST but who knows what will happen while I'm at the boutique!
I would definitely recommend a jumbo black caviar. I think thats a staple and you will get lots of use out of it. It is not the maxi size so not too big so you can use it as both a day and a night bag!!
Also, since it is caviar, it is very durable, I know many people who use it as a travelling bag because the material is very hard and sturdy!