Most people here know by now I am a huge Carson fan. I'm also a closet Obenauf junkie (just don't tell Kit

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I've handled marlowe's but never have owned them. The ones I have handled were well built and well finished. They tend to be thicker and almost "overbuilt." That is not my personal taste, but by no means takes anything away from the quality. Some of his slim modles caught my eye and I wouldn't shy away from one if the right one came my way.
My first custom folder I ever owned was a Carson medium M4. I have sold and traded many Carsons throughout collecting, but this one has never left my side. There is just something about the medium M4 that I absolutely love. For me, it's the best folder design I've handled. I currently own 7 or so Carsons (i lose count) and at least 5 are folders that get used/carried. They have never failed under any circumstances and the fit and finish is always top notch. The knives function as a good knife should, and Kit has the best customer service I have seen.
I currently own 2 Obenaufs and 2 on order (one with mike and one through Joel Pirela) His fit and finish is great and the knives function beautifuly. I have carried/used both of the ones I currently own. I would never hesitate to trust them in any situation.
So, to sum it all up... If the knife is going to be a user, any of the 3 will serve you amazingly well. Pick the one that fits your hand and pocket book best. If possible, try and find away to handle examples of all 3. Buy the one that speaks to you.
If you want something to collect and pass down, buy a Carson first. I don't doubt the others will have collectibility and great desirability in the future as well, but from a collectors point, the secondary market on the Carsons is well established and strong. And that is a huge area to look at when selecting a custom for investment/collectability.
My suggestion is buy one to use, and use it well. It will do everything you a knife should do and never let you down doing it. Also, I can reccomend any of the three because I know Mike and Kit personally and have met Charles at Blade. They are all three stand up individuals, and that is as important as the knife they make.
JR