There's a few reasons for a failed seal--sometimes bits of food get caught between the sealing compound and the jar rim, sometimes the rim of the jar is uneven or nicked/cracked, sometimes the rings are too loose--or too tight (I tighten to just past where I meet resistance and usually do ok). It needs to be tight enough to hold the lid down, and loose enough to let air escape during processing (which is what creates the seal and keeps your food fresh).
Check the rims of each jar, sometimes there's an obvious bit of food, sometimes you'll notice roughness or a chip if you run your finger around the jar rim. Wipe the jar rims really well (I do it twice just to make sure I get any stickiness or food bits), apply new lids that have been softened in hot water for about 5 minutes, and water bath them again.
If you still have problems, mark the jars that don't seal and use them for other food storage (like for dry goods in your pantry). I have a few pretty antique jars with barely chipped rims that I've sanded down smooth that I use for pantry storage rather than recycle them (because I like them)
