Which method is better in achieving depth of field effects for cameras?
1-using the cam focus settings
OR
2-using the cam/lense/depth of field settings?
The Focus Settings has “Draw Debug Focus Plane”, which color codes 3 main aspects of the DOF. Have you read the docs for DOF yet? I suggest doing so, and while reading, keep the editor open with those settings visible. I read it all without doing that a few times, and I keep forgetting some of the settings and what their functions are.
In addition, in the Camera Focus Settings, two of the settings are disabled and the docs probably give instruction on how to get those enabled to tweak them (Current Focus Distance and Current Horizontal FOV). It’s also probable that the two sets of settings work in conjunction, but not sure how.
You might look ath this video here, that explains the basics, how the camera works and how you will get your depth of field. Also there is a fourth aspect, the sensor size plays a role too (bigger sensor, more dramatic depth of field effect, see video at 2.40min). In the video, he also mentions, how it should work with the normal camera:
Thanks alot for the info guys
How about the the other options?
The DOF settings, with Advanced settings hidden, look easier to start from, in my perspective. What is the function of it in the scene?
arch viz/film set scene
Well, in the end, it comes down to what is easier to learn for you. However, with Archviz / Film stuff, you might be better with real world camera settings, since then you can ask real world photographs, what cameras and lenses they use, and then recreate them within UE4.
Here made a quick test to see, if i can get some blur. (looks like i went with a horribly wrong lens for interior filming, but it got blurry ^.^ and it was easy to duplicate this cam)
Oh, and the part at 2.40 where i get confused by that different view… yeah, i forgot that you see the camera meshes in editor, and her the first camera mesh was obviously blocking the second camera. Switching to Game mode should be a thing, would save some confusion :o
Also, have seen, that you wanted and easy method to copy camera settings for different cameras. Well, If you create a new camera, adjust all settings in this camera instead of post process, and then duplicate this camera, all those settings will be duplicated too. All the info is stored in those cameras, rather than just in post process.
Or maybe you can use Material Parameter Collections for this too, would be interesting to know.
Edit: Or take a look at this tool for property transfer:
Thanks alot for the info !
In the video you post did you leave the DOF settings (under the post process section) to their default values?
Yes, no post process settings were changed, also there is no post process volume is in that scene yet 
This is basically a brand new level with just some cubes added, then the recording started. All the settings i changed, are those, that you can see/witness in this video clip.
Also, if you plan to use those camera settings more often, then you can think about making a blueprint or an interface, through which you can control those camera settings easier:
You would “just” need to bind the relevant settings to your UI, like its shown in that clip. I would just rename FOV to Zoom, and invert its slider ^.^