1) DME should be slightly cheaper.
2) I can't taste the difference.
3) I use mostly LME because I cannot seem to use DME without making an unpleasant to clean mess. That's the only reason I have to use LME, but it's a big enough reason for me.
4) When using LME, I use the entire container, adding DME for amounts less than the next LME container. I use up to 6 lb of grain, so that means I use DME only when I'm brewing a big beer, or those where there is not a comparable LME for the DME.
4) I am willing store a partial bag of DME, but not a partial LME containers.