Seals and Judgements are very different, mechanically. I don't like mixing up completely separate skills on a single action button. It's more of a personal preference thing, I guess - you can certainly teach yourself to use any system - but it's like putting Eviscerate and Backstab on the same keybind; it just doesn't make logical sense.
My Paladin key layout is as follows:
1 - Autoattack
2 - Judgement macro
3 - Seal macro
4,5,6 - Primary attack skills (depends on spec)