Keep both. I compared the Last Of the Mohicans on both DVD and LD, and while the DVD beat the LD version hands down on DVD, sound quality of the LD was better - low end had more timber and punch. You can't get some movies like Raiders of The Lost ARk and Star Wars on DVD, yet. Pioneer has some DVD/LD combos that you can get used, although you won't be able to get the latest progressive scan machines.
DVD vs. LD visually.
I'm about to get some DVD player(only visual quality I do care for) and think about getting some DVD collection. I have LD player and certainly small LD collection of my favorite Holywood and none-Holywood movies. Does it make a sence to sell my LD player with collection and get DVD?