I think a lot of people jump right to LV when they first start getting into designer bags, which can be the right decision, but there is no reason to avoid "trendier" pieces. Obvioulsy you should avoid it bags (event hough I feel like there has been a shortage of them lately), as well as anything that Dior makes (its like a car, the second you take it of the lot it drops in value completely--value in this case being "in"ness). I think the YSL Mombasa isn't a bad idea, but that, to me, isn't exactly a beginer piece. I think a Marc Jacobs Venetia would make an excelent first (its a good medium-large size, reasonably classic, and the quality is good). Also maybe the Celina Boogie bag in a classic color (black, tan, etc) would make a pretty good choice. Going back to LV, the Epi Speedy is actually a very very good option. The price isnt that bad (I think they go for like $695 in the new soft Epi), it is completely classic, and comes in a sh*t load of fun colors. Have fun shopping.
matt