graphics
I applaud everyone who has used vinyl graphics on their aircraft, and thought it was easy. It is quite a challenging surface, with compound curves, lap joints rivets etc.
I would caution that perhaps 'graphics are graphics' is a bit misleading.
...sorta like 'paint is paint'. would you use house paint on your RV?
While most graphics providers are knowledgeable and professional, the other 75% that I've encountered aren't technically informed about their product.
by all means, use other aviators recommendations, your local paint shop, etc.
large graphics when designed to fit the shape of an aircraft start to use up many square feet of material, and some will use inferior product to keep the price down. I would expect fully half of the cost to be for design, just fitting to the structure, avoiding compound curves etc.
'Name brand materials like 3M, Avery, Oracal are good to look for, as well as ensuring the vinyl is a 'cast' formulation, usually 2 mil thick.
3 mil or thicker is usually a 'calendared' film, and will shrink and crack eventually.
If you are having images digitally printed onto a base material, that's a more complex issue, with laminates and ink longevity to consider.