The Quake people are telling me they use the 3D editing mode in TrenchBroom exclusively, and the 2D viewports are just an afterthought. These people are the most intense CSG mappers in the world so I think I need to listen to them.
I know this is old, but I use Source 2 Hammer from time to time, which although is mesh based and not CSG based I do have to say, I mostly agree with them... The 2D views are occasionally useful for lining things up and ensuring everything is on the grid, but 3D is so much more powerful in the general case. This is the default setup DOTA 2 and HL:A use. (Note it is Optimized for Ultrawide monitors by default, so you do need to do a bit of size adjustment)
Editor workflow discussion
in General Discussion
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I know this is old, but I use Source 2 Hammer from time to time, which although is mesh based and not CSG based I do have to say, I mostly agree with them... The 2D views are occasionally useful for lining things up and ensuring everything is on the grid, but 3D is so much more powerful in the general case. This is the default setup DOTA 2 and HL:A use. (Note it is Optimized for Ultrawide monitors by default, so you do need to do a bit of size adjustment)