What's your favorite letter of the alphabet and why?

[Saimeren]

I do like ï for it's eye-ee pronouciation.

I am sad when I see people neglect to use it when they write "naïve" because when they write "naive" it's said "nayv"

Only if you're speaking/writing in the original language of the words origin. Otherwise you make due with the phonetics of the language you're speaking/writing in.

That letter doesn't exist in the English alphabet, therefore it wouldn't be used when speaking or writing the word in English.

If you did, you'd just be inserting a random foreign language word into the middle of your sentence. Which; phonetically and grammatically; is not correct.