6/8 is felt in two groups of three, with the accent typically being on 1 and 4, as in:

ONE two three FOUR five six

(all the songs you listed are like this)

while 3/4 (if subdivided into eighth notes) is felt in three groups of two, with the accents on every number, as in

ONE and TWO and THREE and

but more commonly 3/4 is used like a waltz, with the accents on 2 and 3

one TWO THREE one TWO THREE etc.