I am a bit of a VANCHI addict! I have the Joplin and the City Sling (and a clutch...) and love them all. The Joplin is a great size and becuase its longer i dont find myself digging through to find anything, i tend to use it for longer outings. I use a carrier most of the time so use the sling a fair bit as its a bit smaller, but still big enough to fit what i need for a short trip. I have been impressed with the quality of them both and love all the accessories that come with them. I love walking around knowing i have everything i need but not looking like i am carrying a dorky nappy bag!
I have been looking at the Zeppelin for a while now too as it looks gorgeous! Dont know if i can convince DH that a 3rd is necessary... :-)
I also was really happy with the customer service i got from them when i had a question which always makes me happy.
All in all, of all the bags i looked at i thought VANCHI were the best both in style and value. I can absolutely see myself still using them after i dont need a nappy bag anymore.
Hope this helps you decide.