Just my opinion but I think the accident investigation one sounds good. Wanting to be a pilot myself, it would be my opinion that something that shows the ability to solve problems would be useful for the future! Although design is in effect solving problems I would see investigation as being a more methodical approach to things.
As for the LEA looking bad on your CV (think that is what you meant) I disagree, at the end of the day as long as your references are good from previous places of work, it shouldnt matter who they were!
Hope this helps, but remember they're just my opinions!
Ash