Is it better to specifically tweak the image in-camera with its settings to achieve the look I need or it is better to leave the tweaking in post? I am looking for minimal loss of quality.
If you can be certain that after setting the look in camera you will not need to do any further tweaking, then doing it in-camera will yield higher quality results, as the color and gamma correction are done before the video compression.
The problem is, that you can't really be sure if further tweaking will be needed, and that if you go for an extreme look in-camera there's not much you can change in post to take it back without loosing a lot of image quality.
The safest way to go is usually to shoot with the correct white balance (some people say that with the HVX200 you want to shoot slightly bluer than normal and correct in post, to overcome the video compression of the red channel), and with a correct exposure which will retain as much detail as possible. (Remember never to over expose as clipped image in video doesn't retain any detail).
Then, when you have an image that is the most detailed as possible, you can tweak it in post to look the way you want it to look, assuming that any "look" will retain a bit less detail than your original balanced image, you can understand why shooting with an in-camera "look" could prove dangerous if you end up not liking that look. Furthermore you will almost always want to do some tweaking to get certain shots to better match.
A good idea that will help you retain quality through color correction is either doing it in an uncompressed domain, or using CINEFORM (www.cineform.com).