SEO and development both have a good future and It depends upon you that which one is easy to understand for you. It also depends on your interest.
What exactly do you mean by development? If it means as my basic understanding of it then I think a combination of the two is best. This is because no matter what we do we are going to need search engines for online audiences. However development of online marketing strategies must be implemented and one of the places to target most is the search engines because many people are on them and spend a lot of time on them.