Definitely the Vibra Groomer II , although that generic 4 brush agitator is quite a good performer if it's outfitted with the genuine Eureka brush strips.
I've never used a VGI, so I can't say which I'd prefer, but on the hotel grade carpet we have in the living room, the VGII my Sanitaires have do a superb job of cleaning the floor and making it look all nice, but as they're commercial cleaners on what is commercial carpet, they're in their element here...
A VGIII is basically a 4-row version of the VGII, the differences being the beaters are not there, and the brush strips have fanned-out bristles and have bristle stiffener wedges, they're for PNs only and will just burn belts on Eureka & Sanitaire uprights no matter how you try to modify them...
VGIII pic (well, a VGII axle & bearings modified to take a VGIII brushroll tube in my Eureka Rotomatic PN):
I like the VG1 - with the beater and the after market version without the beater bar...both work extremly well.
The VG2 also works very well!! If it is a Eureka...it will clean!!!! Even the old standard wood brushroll with the plastic beater bar cleaned well...the old Disturbulator would as Hans Craig would say "tear up any rug and clean it"
There won't, they cause the belts to burn out (no matter whether it's a Hoover Senior/convettible or the original Eureka RD belts), so there will never be an upright version of the VGIII...