I don't have the Under the Roses deck, but from what I've seen online and some of the reviews I've read, it might not be the best beginner deck. It's definitely beautiful, but a few of the cards are a bit more ambiguous than I like.
I think a Lenormand deck should have very clear, uncluttered images in which the symbol is the prime focus and the very first, if not only, thing you see when you glance at the card. This becomes very important when you get into the larger spreads, especially the Grand Tableau.
For example, both the Snake and Book cards in Under the Roses prominently feature a woman. When I first glance at those cards, I see the woman, not the snake or book. If I'm reading quickly, that could throw me completely off. At a minimum, it could subconsciously influence my reading.
Similarly, I prefer the image to primarily evoke the traditional meaning of the card. In Under the Roses, the Whip card shows a woman in dominatrix dress. While sex, and particularly sex with "whip" overtones, can be one of the interpretations of the Whip card, in my experience, that card is more about fights and arguments, often ones that recur. It can also mean repetitive actions (which can include sex, of course), and -- to bring in the aspect of the broom, rather than the whip or birch rod -- a clearing away (of emotions, usually, but also possibly of dirt or clutter). So, while I certainly wouldn't call the dominatrix wrong, to me, it doesn't evoke the primary meaning.
Once a reader has gotten very comfortable with the core meanings of the cards, the clarity of the images becomes less important. I know many readers who love Under the Roses for its beauty. For the same reason, I'd stay away from "theme" decks art first, too.
But, to start out, I'd strongly recommend a deck that sticks very closely to the traditional images. There are many to choose from. My personal favorite beginner deck is the Piatnik. A lot of people swear by the Dondorf, Stralsunder, Blue (or White) Owl decks. If you prefer more contemporary art, the Zingdoodle deck is great (though I'm not sure if it's still available), as is the recently released Maybe Lenormand (which includes a bunch of cards from other traditional fortune-telling card systems, but you can simply remove those to make it a Lenormand deck).
This site
http://www.wanderingoracle.com has a couple of decks based on older decks (the Wust and Stralsunder) but with very contemporary coloring. I like their Wonderwust deck a lot -- the way it's colored makes the symbol really pop out so you can see it easily. They also have a deck (I think based on the Wust) you can download for free and color however you want to make your own deck.
Ultimately, you should use whatever decks you're comfortable with. Just bear in mind that, unlike tarot, the symbol is the important part, not the art or your intuitive reactions to the picture.
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