I would personally go for wildlife sound recording. You will have a lot of freedom and get to visit places that you never thought existed. All wildlife work requires a lot of research. I remember hearing a photographer state that a particular eagle defecates just before it starts to fly, making it easy to predict when to be ready for the shot. If you know these things you can capture the sounds more effectively.
When you are working you will need a lot of patience and often will be pushing the equipment to the limits of its abilities. But you will be capturing unique experiences.
You would be surprised how often foley is used for nature documentaries, and another person out there capturing the sounds for real is bonus for us all.
Also creature sound design relies heavily on wildlife recordings, and the wider range of sounds that we have to work with the better. So even if you do specialise in wildlife sound recording you might still be working in game audio development.