I recommend decent spd shoes and pedals that suit you. For me that means Sidi Giau or similar and two sided spds (like the ones BigAura linked to).

On the Trans America, my daughter used a pedal with a platform on one side and a spd on the other. They were OK, but I think she said if doing it over she might choose two sided spd for long tours if she already had them. She preferred the platform spd combo ones around home and on campus. Shimano makes nicer pedals that are similar. She found that they cost about the same per mile because they lasted longer

There are lots of other acceptable choices, so it is hard for anyone to say what is best for you.