If I want to connect the 2 meshes on the left and right, what’s the best way without changing the existing meshes themselves and without creating tri’s and ngons?
If I go with the bridge edge loops, it creates tri’s, loads of them, I suppose I can fix that by adding more lööps, but I’d ideally want something that doesn’t affect the left&right meshes.
if you are unwilling to have ngons then at least 1 triangle is unavoidable in your example.
If you are going to be using Subdivision surfaces the ngons will get subdivided into quads irregardless.
In organic subdivision modeling, where should you use ngons and where triangles? Pixar has your answer:
Last but not least I’m going to leave you with this example:
I’m mostly interested in cars with this, so which would be the most efficient and fastest way for cars and similar stuff?
Leaving meshes like this will leave you with a bunch of headaches down the way, especially with surfacing and artifacts along curved and subdivided surfaces. This type of thing isn’t always avoidable, but can be mediated by finding other areas to terminate loops where their impact is low. A larger example would be better in showing this.