Descriptive studies tend to be easier for me. However, Its not about level of ease or difficulty but about applicability. Besides, research is not difficult, it just requires systematic thinking and an open mind.
I think "easiness" shouldn't be the overall focus in choosing research design rather appropriateness of the design in addressing the problem under investigation.
However, ease or difficulty of a particular research design is relatively link to the experience & skill of the researcher and the nature of the problem being investigated.
Waiting for the opinion of more experienced researchers here.
It depence on the problem nature. Easiness also depends on expertise. What is for you might be difficult to someone. So the problem under investigation suggest the kind of research design suitable for it. You can find out from the literature.
Research always is researching what we don't know. Thus, a research project always comes from a research question, a research problem. It does not come from any kind of previous "research design" which means the methodological or technical tools mobilized to address the research question or problem. Therefore, there are no easier or harder "research design" processes since they depend on your capacity to elaborate an original research problem. This is the most difficult. It is easier to replicate available research published through papers, books, etc., but this not scientific research but a copy and paste system that cannot be accepted in Ph.D. thesis, academic papers, or conference proceedings. Research design is a process as follow: 1. presenting the background of the research; 2. presenting the research question; 3. Statement of the problem; 4. theoretical and conceptual framework; 5. Significance of the research; 6. Scope and limitation of the research.