When you and your partner find a 4-4 fit in one suit and a 5-3 fit in another suit, you typically want to play in your 4-4 fit.
When you play in a 4-4 fit, a ruff in either hand provides an extra trick. Playing in a 5-3, a ruff in the short hand provides an additional trick. You would need to ruff 3 times in the long hand (a dummy reversal) to get an extra trick. The flexibility to use a ruff in either hand to gain an extra trick makes playing in a 4-4 fit more attractive than playing in a 5-3 fit.
A second advantage of choosing your 4-4 fit rather than your 5-3 fit is the potential of your 5-3 fit to provide discards of potential losers. The following hand illustrates the benefit of the 5-3 fit providing discards when playing in a 4-4 fit.
Playing in your 4-4 heart fit, declarer can discard a club loser on a long spade and win 12 tricks: 5♠ + 4♥ + 1♦ + 1♣ + 1♣ ruff. Declarers playing in their 5-3 fit can avoid a club loser. They win just 11 tricks: 5♠ + 4♥ + 1♦ + 1♣ .
The flexibility of gaining a trick with a ruff in either hand and the ability to use winners in a long suit to discard losers make choosing to play in your 4-4 fit more attractive than playing in your 5-3 fit.