I would have to say damier saleya pm. I have the azur but I only use it if I'm sure it won't rain. Otherwise it is the right size for me and can be handheld or worn on the shoulder. It can be dressed up or down.
Wow, tough question. Ok, is this question limited to just LV's? If I had to choose just one LV bag to use for a year, it would be the Stephen. It's a great every day bag because it can hold all my son's things, be used over the shoulder or handheld.
If I had one it would be an ivory embossed Steven *swoon*, but I don't so probably my red epi speedy 25. Great size, easy to care for & a nice pop of color to cheer up even the worst day. The very second that year was up, I would toss all my bags in a pile, roll around in them crying with joy & then switch all contents from the speedy into my Nimbus.