Enki is by far my first choice. I bought Live Ed! a year before starting 1st with my oldest to take my time and look at it, and quickly decided it wasn't what I wanted. We ended up using Christopherus for most of Kindy and all of 1st, and although we enjoyed it, I felt it was very light and not quite rich enough. Although there are detailed instructions, it almost had an "overview" feel to me throughout. It just wasn't deep enough for us, though it did provide a nice gentle year that ds1 and I both enjoyed.
For 2nd we it the bullet and purchased Enki, and now that I have all the materials and am figuring ut the lay of the land, all I can say is I really wish I would have used this program for K and 1st. The stories really meet the child with where they are at developmentally. I've learned so much already about what my 7 1/2 yr old is experiencing and what he may be going through and we haven't even begun the year yet. And you can't find Nature stories for science in any other program. The Nature stories, in my opinion, are the best part of Enki.
I purchased Christopherus' From Nature Study to Science and it gave an overview of the way nature stories and crafts give a solid, developmentally appropriate foundation in Science and how to approach science in a holistic way with a young grades child, but it did not include really any actual stories. Instead it listed out-of-print nature story books to buy that I had great trouble tracking down. While on the search, my science and nature loving son was asking me more and more questions about science. Enki has beautiful, rich, detailed nature stories written by the director to use with your child. There is just nothing else out there like it, at least nothing that has turned up in my endless searching.
HTH!