I'd recommend getting some samples online or stopping in to a John Lewis or Selfridges or House of Fraser if you can to try.
Guerlain scents are classic and interesting, but I'm more familiar with (and addicted to) Hermes.
The Merveilles ones (there are several varieties: blue, amber, etc) are all very nice and good day-to-day scents I think. They smell great, adult, and yet not like everyone else, so a really nice investment, and slightly more accessible price-wise than some other Hermes.
24 Faubourg is a serious classic for when you want that "I am a grown-up woman" smell, with a grown-up price to match. Galop is just an amazing fragrance (rose and leather and 'oriental') but so pricey. Twilly is lovely and fresh but definitely aimed at a younger (20s/30s) type of customer. I like it on others, but feel like it doesn't work for my more, um, shall we say mature self?
Thought I would like the rhubarb one more than I did; it's definitely different but I think a bit too fizzy (albeit not sweet) for me. Love Neroli Dore though, perfect summer scent - but if you have other neroli-ish fragrances, this one may not be different enough to merit purchasing. Orange Verte isn't kidding, it's definitely ORANGE and GREEN, very in your face but wonderful. Love it on others, can't quite do it on myself.
Hiris is classic and wonderful, a papery iris as posters above say, but perhaps a bit cold in some ways? I love having it for occasional wear, but wanted something a bit warmer for an everyday scent.
Of the various Jardin fragrances, each one has its devotees. I think the Nil one is the most wearable (and I think it's the one that sells the most), but I may have fallen in love with the new Lagune one. Monsieur Li has very loyal fans.
Have you looked at some of the fragrance blogs/sites? I find that Now Smell This and Bois de Jasmin do enough reviews and get enough comments that it helps me narrow down what I want samples of.