Hi Mjn2ts (funny first name!)
All the Märklin rail choices are OK. Here is how I see them:
M-Track+ easy to find and cheap but inspection of 2nd hand purchases necessary.
+ goes real well with an historic flair to layout (like in the 50s)
+ perfectly compatible with digital operation
- difficult to make long detection stretchs
- may rust in humid environments
Note: avoid large lantern track pieces
K-Track+ flexible track allows any elegant curves
+ track geometry allows more compact layouts than with M or C track
+ under the table switch motors (option
* must ballast the track: allows for more realism but more work
- contact issues when ballasting with glue
- rail size and general track design very much dated (like 20 years ago or more). Huge rails code 100
- motor fixation to switches very unreliable (except for fixed layouts
C-Track+ by far the best: more realistic, more reliable allowing for very nice layouts
+ in full sync with latest Märklin designs
+ can do any long detection stretchs
+ the only offering intelligent switches (motor and decoder in track bed).
+ rolling qualities simply not comparable with M or K tracks: trains just go straight and smooth (no dancing on rails but pure translation)
- more expensive
- no flexible track
- no sleek double slip switch
I have used all 3 types and even have some pieces of Modellgleis 3800 and 3900 but now I stick to C Track
Just my viewpoint
Here is a short glimpse of my layout (sorry for the mess

)
Cheers
Jean