I like the "medium" adult-sized ones. When I first started sleeping with pacifiers about 4 years ago, I used toddler ones, but I found that the short nipple caused the shield to put pressure on my front teeth. I switched up to the Rearz size 6 ones and have never looked back. They're totally comfortable, stay in all night, and I have no more tenderness around my front teeth. As an added bonus, they're also cheap as dirt, which is great because I can have a bunch of them and rotate them and clean then regularly, which also seems to make them last longer. They come in every colour imaginable, too - I probably own 25 of them now.
However, I tried their size 10 pacifier on an impulse, and that thing is too large. It presses so far back on my tongue that I feel compelled to swallow, and I end up suckling on it just to avoid feeling like I'm drowning... not relaxing. I don't use it much.