Garn,
No doubt you are considering your temperment while evaluating design vs. line work options. Line work favors those who prefer discrete, physical, linear tasks with a clear beginning and end and relatively immediate feedback; design work those who can work in a more abstract internal way and can tolerate delayed (or the absence of) feedback. Line work provides greater opportunity for travel or unique locations while design work is more of a stable office environment. (Sort of a “Car Talk’ vs. ‘Office Space’ comparison, if you are familiar with US entertainment.) That said, I almost always prefer designers who got their start in the ops world – these folks think more holistically, can quickly orient themselves on the platform, understand the interaction between the component they are working with and other systems and the user, and understand the cost of doing business (especially the costs when things go wrong). There also seems to be a mission focus often lacking in those who have only operated a desk.
As for promotion, I suppose that depends on what you mean. If by this you mean money money, I suggest you look elsewhere as aviation is like an NGO, where you are here because it is something you love and not for the lifestyle. That said, aviation is usually a meritocracy, where knowledge is key. It’s like ericferret says, a true professional is always learning, and this is what generates advancement. And if you start off on the line side and decide you would rather be driving a desk (or vice versa), you can always do change course. That’s one of the wonderful things about aviation… if there is a specific subject that interests you, you can always create a niche.
As for writing the checklist versus using the checklist, a good designer will always validate their work with someone in the field prior to publication.
Best of luck to you, whichecver path you choose,
Jolly