OK this is my opinion on both decks for the purpose of reading. It closely resembles Umbrae's.
I love Lenormand cards because to me they read easily and once you have the general meanings for the cards you can then adapt them to your own experiences. You can lay them out and read them from the picture. Although if you want to read the Lenormand spread, which from memory uses the whole deck, then it takes some practice. At one time I was involved in a Lenormand Reading group:
Lenormand/Titania Weekly Draws - Index
I learnt a lot from this group and the constant weekly readings that we did.
The Etteilla deck is like a forerunner to Tarot. The cards are in a different order, as I said before, in that they are numbered 1 to 78. I think we all have our own views of what the Majors mean to us, and whether or not they are in the same order makes no difference to the meaning of the card perhaps, (except maybe if you are a Capricorn, and then order is paramount
). I think what I find most difficult about reading with the Etteilla is that the pips are quite sparse. When I read the pips of a Marseilles my imagination plays with the foliage. I just don't get the same creative vibes from a deck without the foliage, and the implements are usually arranged in a quite predictive way whereas the Marseilles ones aren't necessarily.
For example, the Nine of Coins Etteilla compared with the Nine of Coins Marseilles:
.............
I don't know if this has been of any help in your decision of which deck to buy. Personally I would get both, but if you want to read straight away then the Lenormand will serve you well and it's a really great deck.
Both decks will encourage you to explore the history. Both are important historical decks, which is why I cannot compare them as such.