Shall I keep those general prestigers w/o STAB moves?

if you don't use them, no point of keeping them. And even if they don't get STAB, sometimes you can find a SE matchup that it can benefit from. and if it KO's then you can just transfer if you think your revives are too precious. . .

Some of my Pristegers even with High IV are been transferred. I usually use a newly caught Pokes as pristegers then transfer...

Yeah, unless you're desperate for space I'd always say to hang onto things. If nothing else you can use them as one-off battlers and save yourself some potions/revives. When it comes to prestiging it also helps to have as big a range in your CP pool as you can.

Golduck is a WG/HP prestiging hero. Otherwise unless it's a great IV I got to use it 1x and dump it. lol #spacehogs

I always want STAB on my prestigers. It effectively increases the Attack stat by 25% without increasing the CP -- essentially, you get a "free" boost in attack.