Your measure of best is a bit limited. For my money "best" should include:
readily obtainable materials
high printing speed
large build volume
easy to build, calibrate and maintain
robust/transportable without loosing calibration
compact (relative to print volume)
easy to enclose (for a heated chamber for ABS or to exclude dust)
capacity to add multiple extruders, either direct drive or bowden
capacity to add light weight machining head
light weight - if you plan to move it around. Heavier if you want to limit the effects of vibration.
You can't maximise all of the above in one machine. Dual direct drive extruders will be heavy and can't be moved fast. A fast delta machine is not particularly compatible with a direct drive extruder so is less suitable for elastomeric (flexible) filaments (and deltas are excessively tall compared to print height).
I haven't built one yet but my favorite mechanism at the moment for my next large capacity XYZ machine is CoreXY. The bed only goes up and down (slowly) and the X-Y mechanism is fast. With XYZ machines like Prusa i3 having the bed moving fast means that the overall machine speed is limited. Also if you do a large print on your moving bed - the moving mass increases and can reach a limit where you skip steps - absolutely the last thing you want to see near the end of a 3 day print! With CoreXY the frame can easily be enclosed and the build volume is large compared to the overall volume. I would bowden feed a diamond hot end if I needed multi-extruder capability. I'd do a quick release hot end so I could replace it with a direct drive single hot end to be able to do flexible filament or a dremel tool to be able to do light machining or PCB drilling.
My Prusa Mendel i2 inspired Repstrap with welded steel frame: [youtu.be]
And my Smartrap derived Briefcase 3D printer: [youtu.be]