If you're only looking at CB vs Pot, then it really depends on your stats.
Spell Dps/ Spell Healers - You want to even out your CB/Pot ratio. They are multipliers and boost each other the higher they both are. Example: 5x1 = 5, 4x2 = 8, while 3x3 = 9, etc..
Melee Dps / Melee Healers - As autoattack is a good chunk of your dps, you should prolly lean more to CB. However, if you're playing a Melee Healer (chan, inq, myst, warden) and not meleeing (sadly, some do this), then either betray or gear as a Spell Healer.
Tank - This is dependent upon your performance. If you can't keep threat, increase melee stats/CB [Crusaders may want to even out CB/Pot here as they cast a lot]. If you can't survive, increase tanking stats (I'd suggest Mit here, but avoidance [block/parry/dodge] work too.)
Note, the special spots Cheesy mentioned (Flurry, Doublecast, Mit Increase) only get one slot, so if you aren't capped for it you should probably use those on the correct classes.