More spins have lower variance but the payout should be the same regardless. Similar to the topic is the Osbournes random "pick a present" feature. I always used to go for the Ozzie's gift (the farmost right one) which is biggest variance and therefore has a largest span of potential return. However as I never got anything over 2x on that (which is the minimum) I devised a cunning strategy of closing my eyes and clicking randomly. I concluded that the payouts are much better that way.
Dolphin tale is one of my favourite slots (for payouts anyway) the variance doesn't seem too steep, and I've hit the feature plenty of times. It's got 5 choices for freespins, and based on my results I've had the best luck with the fourth option 10spins at 5x/8x/12x multiplier. When I've gone for more spins, I've found it to be less generous, just my 2 pence though.