Hard to say. I would lean towards your bro's friend. Do you know him well enough to answer these questions:
Does he normally pay his bills on time?
Is he a clean person?
Have you been to his current residence? Can you assess whether he would look after your property?
Why is he moving?
I would also make him pay the higher amount as I would be inclined to believe he is just trying to get a cheap deal from you. You can always tell him any less wouldn't cover your repayments so you just can afford to drop the rent.

DOH might be more likely to pay but do you get any right to veto their tenant? You just don't know who the DoH will let in IYKWIM. I would be scared that they would put in the type of tenant you see on ACA. I know that type are the minority but you have to consider the possibility.

Having said that, in both cases, take out landlord's insurance. It's not expensive and will give you peace of mind. Also make sure your agent does a reference check.