I like DME because it keeps really well. LME is fine too so long as it is fresh. I've found that many of the kits containing LME, at least in my area, are pretty old. I've seen some that I believe are more than 5 years old.
About 15 years ago I brewed a beer using LME that my father had sitting in a corner of his house. At the time I didn't have any clue about freshness of LME and yeast. These cans where over 10 years old at the time and the yeast I used was just as old. Looking back on it, it's truly amazing it even fermented. The beers that resulted from these old cans of LME nearly turned me off of homebrewing completely. I know now not to make beer with 10 year old LME, Hops, and yeast. At the time I just thought I was incapable of making decent beer at home.
*funny story about that beer -
I had a friend insist on trying a bottle. I tried to talk him out of it. He shows up at my place and brings a bottle of some beer he made a year earlier. He starts telling me about how he made it. His ingredient list and method was such that it curled the hair on my back. I felt much better about letting him have one of mine after hearing about what he made. He takes a taste of my beer and makes the predicted ugly faces. I open up his, expecting it to be as bad or worse, and its delicious. I was so embarrassed.