Answer: That deserves an answer. First of all, in every meter the first note of the measure is the most important. That's part of what defines the meter. 5/4 is 5/4 because it gives the impression that the music is grouped in fives, so the first note will tend to be emphasized either harmonically or melodically.

But there are secondary accents, too. Just as in 4/4 time the main emphasis is on the 1 but a secondary accent is on the 3, so in 5/4 there's a secondary accent as well. But just where it ends up can vary, which is one of the neat things about 5/4.

Let's take the most famous of five-four pieces, Paul Desmond's "Take Five:" I'll simplify the tune here so that the organization is easier to see (leaving out grace notes). A metric accent doesn't necessarily mean there's a big bump on that beat, but that it's set off in some way: a change of harmony, a melodic shift, a phrase break. The 16th-note figures below clearly make an accent, as does the beginning of the slurred pair of quarter notes in the first full measure. But notice that the 5th beat is marked with an accent in one measure, which adds a little ambiguity:

This theme is consistently grouped as 3 + 2, giving some emphasis to the 4th beat as well as the 1st.

5/4 music can also be found grouped as 2 + 3, or in varying groups, so the secondary accent will depend on the nature of the piece.

5/4 is fun partly because it goes against our natural tendency to think in strictly duple or triple; it mixes the two, which can make it hard to keep in your mind at first. I used to live in a place where a neighbor came out on his balcony many summer evenings to play "Take Five" on his saxophone. In 4/4 time. He did it something like this:

My theory was that he played it so often because he was thinking: this still isn't quite right, somehow, can't put my finger on why. It takes some time to get the more quirky meter in your head.