I have an orthophoto, and i want to publish it.
Is it much better to publish it as map service or image service?
what is the difference between them?
what is the advantages/disadvantages for each type?
Which type has better caching ?
A very good blog on this topic Imagery in Web applications: Should I use a cached map service or an image service?
If you want to retain the properties of an image (like pixel values, image enhancement, etc.), you need to publish the image as a image service. If it is just for visualization purpose, you might like to go for Map Service.
Caching will improve the rendering for both Map as well as image service. It is advisable to cache, if the map/image service don't change often.
To add to that, Image Server (or Image Server extension pre 10.5), is an additional license, so that may have to be taken into consideration.
However, even if you end up caching, in my tests, caching of an image service is much faster (~1/8 the time) than caching a map service. Dropping a 8 week cache job to ~10 days, while adding 5 more scales makes it pay for itself, in my opinion. Plus, the Image Server gives you the option to do either.
re: viewing as a basemap. If using a cached service, you will be limited to those scales when creating a web map (ArcMap will interpolate between cache levels/scales). This can work to your advantage if you need to control how users are viewing the maps, but can work against you if you do not have enough scale levels.
These are just my opinions. Results may vary.