I started my bag obsession collecting Isabella Fiore bags when they first came out. They were beautifully made and intricately beaded. I bought four or five over time and never used any of them because I thought they were too special for my casual lifestyle. They were like pieces of art. Eventually I sold them all, putting the $$$ toward new (and more expensive) bags.
I can't remember which designer bag was my first big purchase--it was either my
Prada, which I still love and use, or a Marc Jacobs satchel I ended up selling brand new because it was too heavy. I loved that MJ bag (it was black with pink stitching and a vibrant pink suede interior), but it's size and weight made it the wrong choice for me.
Now I try to limit my purchases to bags I can really use and enjoy. Now matter how much I love the style and look of a bag, if I won't love actually carrying it, I won't buy it (okay, maybe I'll buy it then return it when I come to my senses).
When a bag looks great and fits my lifestyle I never have regret. The best advice I can give is buy what you love, not what the fashion editors are pushing or the starlets are wearing--though you will likely fall in love with some of these bags too.
As for my favorite bag...it has to be my chocolate brown BV woven knotted hobo. This bag has a casual elegance I love, not to mention the softest leather I've ever felt. After carrying this bag for a season I loved it so much I bought the same one in white. If they still made it, I'd buy it in black, too!