I recently ordered Diptyque Eau Duelle Solid Perfume ($48 for 4.05 g/0.14 oz). It's a very soft earthy vanilla. I had tested this a few months ago at the San Francisco Boutique and South Coast Plaza stores. I found it less intense and not quite as sweet as the Eau de Toilette and Eau de Parfum versions. Vanillas can be difficult for me to tolerate so I usually have to do sampling on various occasions by spritzing at the counter and wearing the scent for a few hours. My sensitive nose tends to react very strongly to sweet vanilla scents (in a bad way). It took me several months of thinking about Eau Duelle before I decided to buy. By the time I decided to purchase, all the counters and stores near me were sold out. I could only find it online at Neiman Marcus. Although the Diptyque reps have assured me it's only temporarily sold out, a couple readers have told me that the solid version is being discontinued. At this time I'm not sure which is true.
I was lucky to get a few samples of the different versions of Eau Duelle. The liquid sprays are significantly stronger and sweeter in scent. The Eau de Parfum has an almost incense-like smell to it. The Eau de Toilette is lighter and sweeter. I prefer the Solid Perfume by far as it's the softest, however I feel I may be in the minority in my preference. The lasting power is medium. Since I prefer softer vanillas I don't mind that this one fades within a few hours.
I'm still on the hunt for the perfect vanilla fragrance. I love Serge Lutens Un Bois Vanille on others. It's a bit too dark for me. Others are too sweet or strong. For now the sweeter round scents I like are Tom Ford's Oud Wood and Jo Malone's Dark Amber and Ginger Lily. Not exactly vanilla-like, but there is a slight vanilla-ish undertone to each one (review on these soon).
I'm happy I purchased Diptyque's Solid Perfume version of Eau Duelle, but I'm still on the hunt for my perfect vanilla scent. If you have one you love I'm all ears for your recommendations.