Well I am no authority on the subject however; with Cloud's given personality, Yuffie would be entirely too childish for him.

Yuffie is like Selphie in FF8, "Oooo I like trains." Selphie was too childish for Squall. Same scenario different people within FF7.

As for Tifa and Cloud, Tifa is the childhood friend that has always loved him but he never loved her more than a friend.
-He was trapped to protect her because his childhood vow to always be there. He never meant it to be a romantic; but that's what she took it as.

His actions in Final Fantasy 7: Advent Children demonstrated his friendship, NOT love.
-He sleeps in an orphanage, not with Tifa for one.
-In the scene in which she says the worst line in history (Dilly Dally Shilly Shally), she is awfully critical of him; the type of critical a best friend would be, not a lover.
-In addition if Square-Enix wanted to throw them together, they would have added a kiss in Advent Children SOMEWHERE.

This leaves Aeris; Elegant, beautiful, intelligent, & mysterious. He acted completely depressed when Aeris died; a loss of love reaction he had.

He mentioned her being full of life and him never being able to see that again.
Then he carried on this weight, the responsiblilty of her dying (even though he could have done nothing more) throughout Advent Children; two years later and he was still carrying the weight. It takes just as long to come to terms with being widowed, in real life.

Summary: He had nothing to do with Yuffie (who would think that)
Tifa and him were childhood friends and best friends when
they grew up.
Cloud Loved Aeris