Ender 3 pro / V2 if you wanted to to an Enderwire conversion if you can get it cheap enough but you pretty much only keep the frame, steppers, bed and possibly the mainboard.
Otherwise, as above, go for the full Voron spec / frame as the frame has a much bigger footprint improving stability, no trickery with under unit electronics and you dont have to worry about incompatibilities - you follow the Voron guide and use the voron provided print stl's.
I have a Switchwire and a standard Ender 3 Pro - if I was to convert the Ender 3 over as well I, personally, would purchase the Voron frame and use the Ender 3 hardware where i could rather then the ender 3 frame - just my 2 cents.