I have only ever tried Fearless and Outmaneuver on my Fenns. And occasionally Predator. But I have never used him in a two-ship list. The only two-ship list I have ever really put any time into is Guri/Moralo. And I did use Lone Wolf on Moralo in that one for quite a while, until I stopped. I found that I was mostly using Lone Wolf on defense, where it is so much more likely that I would reroll a blank into a blank just based on the physical facts of the die. And that was only ever just a single die roll on a ship that is just plain expected to die. It didn't feel good. And I found that I was unable to use Lone Wolf rather frequently as well, as I was trying to trap my opponents between Moralo and Guri, trying to concentrate fire. I gave it up and put Intimidation on Moralo. That doesn't trigger often, but it has changed the way my opponents have been flying, forcing them to make suboptimal choices even when they didn't *really* need to.
In terms of Fenn, I think Fearless is the way to go. Every time. Lone Wolf, as you say, may trigger with fair regularity, given the way you fly, but has that probability of producing zero result. And Outmaneuver is so easy to turn off; turrets aren't uncommon. But Fearless is a guaranteed result, as long as you fly right. And further, you know you are going to lose Fenn. He is a glass cannon, a variance attractor. Keeping him cheap is the best policy, and Fearless is the cheapest of those options. Now, if only we put both Fearless and Predator on the Fang....