Although the DS1 MP map is far more interesting, and the enemies are much more varied. Also, for a spellcaster class, DS1 got way more spells (once someone wondered why my melee hero had mana regeneration, oh yeah, mana shield! Such awesome spells aren't in DS2 ).
Aside from that DS1 MP can be done with 8 vs. 4 players (IIRC).
So, yeah, the mechanics of DS2 are more interesting, but DS1 got the superior MP gameplay.