Seeding by hand if well done will get rid of 100% of the seeds. Of course it's tedious & I'd recommend a puree sleeve, food mill or something similar. Most sleeves will remove 98 - 100% of the seeds. Sometimes the tomato skins will temporarily clog a sleeve though.
Some people leave the seeds in (whole, not chopped up). I've been meaning to try this as it would retain the slime that surrounds the seeds which reportedly contains a lot of flavour. The possible problems with this are aesthetics (doesn't matter to me, but might to you) & whether the texture of having whole seeds is objectionable.