mostly depends on personal preference. A smaller blade is preferred by some since it tends to let you snap off quick strokes to catch the waves, whereas some prefer larger blades to give you more power in fewer strokes.
I tend to prefer something a bit on the larger side, Starboard Enduro Carbon 525-55o.
One item most people agree on though is shaft length… You typically want to have something 2-4″ shorter than what you’d use for flatwater.