What would be the most promising of the three approaches here? guess I am not the first to run into this situation 
Any information is welcome, I am new to surface modelling. G2 continuity did not work out very well yet..
what is the difference between trim+blendSrf and filletSrf btw?
What is your design intent? What do you want the result to look like?
FilletSrf works on two surfaces which intersect or are close enough to each other. The width of the fillet is determined using the rolling ball rule. Imagine a ball rolling in contact with the two surfaces simultaneously. The curves of contact between the balls and the surfacesd the edges of the fillet. The fillet surface can have several types including circular arc cross section tangent to both input surfaces, a deformable surface tangent to both input surfaces, or a surface with G2 continuity with the input surfaces. The input surfaces can be trimmed along the fillet edges, or left untrimmed.
Trim and BlendSrf starts with the user trimming the surfaces as desired. Then BlendSrf is used to create a blend surface between the trimmed surfaces with user selected degree of continuity at the edges. The degrees of continuity along the two edges can be different.
There is no clear-cut “right” approach in surface modelling. There are often two or three alternative approaches that can work. Selecting an approach depends on the design intent, the type of surface transition desired, and the model accuracy needed. By trying out different approaches, as you do, you learn for yourself which one you prefer for the design intent you have in mind.
I would say v1 and v2 with blendSrf are closest to my design intent. BlendSrf is set to g2, but I cannot manage it to be continuous in the upper part of my blend.
carfender_question.3dm (3.0 MB)
Hi @eg1
I think you just need to set the quality of your analysis mesh to something much, much finer, see screengrab below.
HTH, Jakob
Edit: Or use EdgeContinuity to check your edges 
Oh ok, yes that looks a lot better! Thanks a lot. 0.001 sounds good, is that good? This is not a actual part for manufacturing obviously…
Whether in production or rendering, if it looks good, it is good.
