I think the dub in Laputa is awful - they've added so much dialogue where there was none originally. Watching in Japanese with the subtitles (which match with the English dialogue rather than the Japanese) was rather confusing as half the time there were subtitles when there was silence.
I always watch with subs where I can, though I did catch Totoro on Film4 the other week and it was surprisingly alright, even if it was Dakota Fanning. I don't like the Mononoke dub at all, the voices are just so wrong, and I wasn't impressed when I saw Howl's at the cinema, which had been advertised as subbed, to find them speaking English.