"Iconic" is a word used a bit loosely in the watch industry, but it may be used accurately with respect to the Historiques 1921, I think. Perhaps no other watch better represents modern Vacheron Constantin.
It is a great watch. This is the one with which I began my hot and heavy affair with Vacheron. It is a great place to start if you can. The Overseas or QdI would also be great watches with which to begin, but since you are asking for opinions, the 1921 would be my top choice. It is beautifually made, wth a lovely size and perfect proportions, classically beautiful, but with enough interesting conceptual and design elements to make it stand out. It is already in its eigth year of production but it is made in relatively low numbers on an annual basis that it remains a rare watch.
Here are couple of photos of mine to make the case (the writ shot was taken by friend Paul Boutros):