For me it's the TRM Neutron hands down.
The MBK is a great knife but the flood of imported, good quality knives has become a little excessive. The Old Guard isn't that much different from a couple dozen other knives available in a similar price range and it seems to suffer from an overload of vanilla. The blade stock is fairly thick so I'm not sure it would make a good slicer.
The Kizer is a significantly cheaper knife. The Vanguard line is a good, budget option but it's a couple steps down from either MBK or TRM. I have a Ti Genesis and it lives in a knife bag.
The TRM is made in the USA in small batches. It has a very distinctive look and stands apart from all the mid-tech, frame lock imports. The blade is the sliciest of the bunch. The one criticism that some may have is that the knife is very thin. With the Atom and Neutron 2 you can buy sculpted scales that change the thickness profile. My Neutron is always in my EDC rotation.
Another knife hitting the stores soon that may interest you is the CIVIV BO. It's a Brad Zinker design and Brad knows how to make a slicey knife. It's priced similar to the Kizer but I expect it to be better in overall quality. Looks-wise its very similar to the Mini Old Guard at a fraction of the price. I'll probably pick one up to check out.
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