To my everlasting disgust, it is the Space Marines.
I don't mind experienced players doing them, but sooooooo many newbes do them just cause they're too lazy to play something a bit more challenging.
Do you really think this is true?
Surely, being new, they don't know what's challenging and what's not? How can they know these things without experience?
I would think that the main reasons 'newbes' play marines are that they've been in every (?) one of the starter sets, the range for them is vast and substantially plastic, they have 4 codices, they are constantly marketed by GW in a way DE, WH and Necrons for instance really aren't, their fluff is awesomely OTT (genetically enhanced super-Nazi gothic warrior monks), they're easy to paint, you can do them how you like (one colour, or decked out like a medieval knight) and they're so much easier than any other army to understand (except IG, who let's face it are quite dull).
All of these I think are much more compelling reasons than 'laziness'.
:trying to be reasonable cyclops: