I would say that it totally depends on where you need another attacker.
Of the listed three, I think the Espeon is the most immediately useful as it is. I know psybeam isn't supposed to be great, but the fact that you can get it off often and still dodge (with Espeon being a glass cannon) makes it still useful as an attacker, I think. Not as good as Future Sight, but not terrible either. I would probably eventually try for Future Sight, but only when I had plenty of charge TM's.
So the Espeon is probably currently the most useful of the three. I probably wouldn't ever use a Heracross without double fighting or a Venusaur without double grass.
With fighting currently being strong in the raid meta, going for a double fighting Heracross looks good unless you already have a Machamp army.
As for Venasaur, great if you can get Solar Beam, but I guess most of us already have an army of Solar Beam Exeggutors making it perhaps not as immediately useful as the other two??
