I own the Imp, Iheat and a diy 510 atty. By the past I got the Project and I have somewhere a DT Gen2 dry herb atty (conduction). They are all nice but all need stirring except if you use a tiny load for 2-3 hits max and when you try to get rid of stirs taste sucks after a few hits. As well convection vaping need you focused on what you are doing, if not the case you end with a poor hit or charring (remenber the TV, you need at least a 40s hit to get decent vapor).
Next step might to work on the association of convection AND conduction on a 510 atty to get the easyness of use conduction vape get with the on-demand feature and quality of taste of convection vapes. All that in order to reduce inhalation duration, focus on what you are doing and harsh hits (coughing).
For now there is no best for me, Iheat for cigar puff and bigger load, Imp for smooth hits and small loads but both are used with a water tool which is, finally, my favourite way to use this sort of attys for now. Actually my on-demand dry vaping is wax pens and I prefer to use differents others vapes for my dry vaping needs, so Iheat and Imp are used quasi exclusively with water tools (I speak actually... before and after it was/will different). My Diy atty is on beta phase and my purpose was to get one 510 atty for dry vaping but without the hassle of stirring...