I have used the gen 1, 2, 3 and 4 HDPE fermenter and got on well with all of them.
It's a journey many of us have made although you forgot to give an honourable mention to the gen 1.5, the clip on lid bucket with a tap! (Ahh the luxury)
@Georgedgerton I'm with duncbrewer on the FS's, if I'm using a conical then the one with the larger valve is my preferred unit, I haven't used the Gen 3 with plunger so can't comment on it.
To really answer your question though you have to look at your process's,
The advent of floating dip tubes on pressure vessels has made oxygen free racking feasible, but nowhere near as convenient as just dumping from a conical, using an all rounder/chubby etc you'll ferment (under pressure or not) then seal it up and use pressure (gas) to transfer off the trub to another vessel, (another all rounder/chubby?) hoping that hop matter doesn't block anything and then onto keg/bottle. So we now have two fermenters to clean and store, you already know how it goes with a conical, ferment, dump, keg/bottle, clean one vessel. You may decide that cleaning two rounders/chubbies is easier/quicker than cleaning a conical, and storing an extra fermenter isn't an issue.
Harvesting yeast is another plus for the conical, but only if you do it.
Often overlooked is physical effort, lifting and carrying 25kg plus, isn't everyone's idea of fun, and using two fermenters as opposed to one will result in extra lifting/carrying.
Maybe you're an extract brewer, in which case HDPE rather than PET might be preferable as boiling water to melt the goop will make short work of any PET vessel.
Perhaps you "like to watch"
I find it strangely satisfying looking at a fermentation in progress, so +1 for PET's.
If you only ever ferment one type of thing using the exact same process every time then perhaps there is the "ideal" fermenter, but I've got HDPE gen 1 to gen 4, PET conicals, FKJ's, a couple of kegmenters, and various glass carboys, what I'm fermenting and how I'm doing it determines which vessel gets used, I wish there was a one vessel does it all, good luck with your quest.