PROs: I can't rave enough about ASOS! I live in Toronto, and I find the majority of their items well priced. Shoes especially are affordable and on trend. Way better than buying something generic, poorly made and overpriced at let's say ALDO or Town Shoes. ASOS is also generally very trendy. I usually find the latest trends on ASOS before they ever hit the malls here. ASOS sells their own brands, and several other third-party brands as well. They range from the super pricey like Stylestalker to super cheap like the ASOS brand; so the quality and worksmanship can vary. I personally like the ASOS brand. The quality is decent to very good; however you can't beat the pricing, especially once items go on sale.
CONs: Admittedly, I have several items from ASOS which either didn't fit well, or look as nice (on me) as they did online. That being said, I still continue to order items from there because for every one item I didn't love, I have 10 that I adore. Another con is the returns, at least for us Canadians. It can cost a pretty penny to send items back to the UK and I would recommend waiting until you have a few (if you order as often as I do) to send it out as one shipment. Outside of that, the returns process is no-nonsense, quick and painless.