What is the best role to have in the armed forces?

I really want to either be in the RAF,Navy or Army and I want to do ether food(cooking,waitressing ect.) Or something to do with Air craft

Field Marshal?

whistleblower

there is no answer based on the information that you have provided. All 3 branches have chefs (or did have but it may outsourced now) and all 3 have aircraft. Even the Army has the Army Air Corps (AAC). The chefs were with the Royal Logistics Corps (RLC) when I served.
the differences tend to be the conditions that you would be working in. I dont know about the RAF but in the Army you can expect to live pretty rough on exercise. You would have a sleeping bag in a tent, possibly sharing with other people. You would be cooking and serving in a big tent although the cleaning is only really your cooking materials. We had to use mess tins and our own cutlery which we kept hold of.
I would imagine that you would be working in a kitchen with the Navy on exercise. I have no idea what catering facilities the RAF are provided with though.
in barracks you have a designated dining facility (cookhouse) for the Army and RAF. The Army has fixed meal times but RAF Brize Norton and Lyneham had chefs available day and night due to the flights coming and going at all hours.

do you now see why the original information is not enough?