RE: your thread title.
My experiences would suggest Spyderco Ed Schempp TUFF C151GTi (a 3v blade in a folder designed with very secure lockup). Ergonomics are stellar in my mind (Ed Schempp design, hmmm

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RE: for your usage description.
It sounds like you spend some work time in a construction type environment. With over 30-yrs practical experience I would suggest Stanley 10-499 (similar to what others have posted previously). One has lived in my bags for numerous decades (always at least one spare too, along with multiple replacement blades in various configurations).
Takes about 2-seconds to change out a blade (fresh sharp blade OR different configuration entirely). Replacement blades are stored in the handle for quick-change as needed.
For carpet (as you referenced), as well as tough cutting roofing materials the various hook blades profiles really excell as they cut from the bottom side. For carpet - means cutting the backing easily from the topside with sharpened edge not being abused by embedded debris. For roofing with exposure faced embedded ceramic granuals - same principal as the carpet, but much more significant.
It would be hard for me to imagine using a cutting tool with a thick blade when there are purpose built tools for utility cutting tasks where a thin profile is so much more efficient.
Stanley 10-499 Open
http://i215.photobucket.com/albums/cc155/ChrisOBucket/Knives/Stanley 10-499-open.jpg
Stanley 10-499 Closed
http://i215.photobucket.com/albums/cc155/ChrisOBucket/Knives/Stanley 10-499-closed.jpg
Stanley 10-499 Blades Options are MANY (more than just tgese images.
http://i215.photobucket.com/albums/cc155/ChrisOBucket/Knives/Stanley 10-499 Blades.jpg
There are a number of handle configurations available (bent, straight, folder, flipper, etc.) with quick-change options and various blade profiles. For overall usage, I prefer the original straight handle but also have angled versions for use depending on application specifics (job at hand).
Hopefully some enlightenment here for someone ;-)
Regards,