Dual at level 9 for the extra proficiency. You'll never get an extra proficiency that you can specialize (or master dual wield) with again. (I would pick two in sling, two in flail, two in hammer or mace, one in dual wield) I also think you don't get spells until level 9, and if you dual before then, I don't know if your cleric learns the druid spells that the ranger gets.

When does everyone recommend dual classing a Ranger to Cleric?

According to my calculations, the best time is at level 8. Here's why? The XP cap is 2,950,000. The game starts at level 7 so a Ranger has 75,000 XP. That means if you dual class at the start, the character can only achieve 2,875,000 XP as a Cleric, which is level 20 for Cleric.

If you dual class at level 8, the Ranger will have 150,000 XP. So the character can only achieve 2,800,000 as a Cleric, which is still level 20 for a Cleric.

If you wait until level 9 to dual class, the Ranger will have have 300,000 XP. So the character can only achieve 2,650,000 as a Cleric, which is just shy of level 20 for a Cleric -- the best then is level 19.

So I think the two options are Ranger(level /Cleric(level 20) or Ranger(level 9)/Cleric(level 19).

Which does everyone think is better. Or tell me if I'm missing something?

Don't know why there was a smiling face in the text, that line should read:

So I think the two options are Ranger(level /Cleric(level 20) or Ranger(level 9)/Cleric(level 19).

I'd recommend a bit earlier, even level 6 or so. Plus the EXP cap ain't a problem if you remove it !.
My personal pref is a multi class Cleric / Ranger.

Obviously doing something wrong -- last try no matter what.

So I think the two options are:
Ranger (level / Cleric (level 20) or
Ranger (level 9) / Cleric (level 19).

I'd go for Ranger lvl 8/Cleric lvl 20 as your cleric skills will end up more important to you by then. Anyway I'm pretty sure you can keep adding proficiencies. When I used Anomen - dualed Fighter then Cleric - and a proficiency came up, I was able to give him a third point in Mace. Once you can use your Ranger class again I'm pretty sure you can put two points in proficiencies where applicable.

The smily is there becouse you enter a code to get them on your topic , you typt 8 ) (whitout space between) you can do this too : .

About the cleric / ranger thing , be a multi class our use the Xp cap remover .

Really? Hmm... Will have to try it then.