PDF reader for iPad with both bookmarks and continuous scrolling, without long save and load times
I have been a happy GoodReader user for many years. Lately, I have switched to PDF Expert, though, since I like its interface better (especially for adding and editing annotations). It is not quite as featureful as GoodReader, though.

Both use tabs to let you switch quickly between documents. I can't comment on the time to open a document compared to the apps you mention, though. Documents generally open quick enough for me.

Edit: Oh, wait: GoodReader doesn't do continuous scrolling, it seems. My bad. It's been too long since I used it, I guess.