Everybody has an opinion which era/country of mfg/type/marking/etc is "best", but really- they're all good. There isnt a "bad" variation that I know of.
Of course, it makes a difference if you are buying it to use or to put in a safe.
Some can't live without an "all Belgian" gun, and that's what I'd prefer to loack away. But I think the "Made in Belgium, Assembled in Portugal" guns are just fine.
Later guns, starting around 1990 or 91 have cast frames rather than forged. Ordinarily, that would be a negative but in the case of the HiPower the cast frames are made of harder steel so might be better for a gun that will be a shooter.
Cast frames are identified by fore and aft serrations around the magazine well.
Forged on top; cast below:
Current guns are known as Mark IIIs, or MKIIIs. They have the cast frame, ambi safety levers, and higher profile sights than earlier guns. They appeared about 1988, give or take a year.
The MKIIs had forged frames, ambi safety levers, high profile sights, and most had a low narrow rib on the slide but I don't know if they all had that. They came out in the mid-80's, I think.
What is now called the MkI by some, is the classic HiPower with single sided small safety, small sights, etc.
Adjustable sights. They've used a few different types over the years, and most aren't very good. I wouldn't pay any more for them...at least on a shooter.
Trigger. It seems like the most common HiPower complaint is a heavy, or stiff, or rough trigger pull. I think they vary a lot from gun to gun, and some come with fairly decent triggers. I had the chance to buy a HiPower from a selection of them, I'd go through them checking triggers and pick the best one.
The trigger reset will be longer than on a 1911, so don't be too surprised if you have to make your finger go back farther after being used to a 1911. It can be helped with gunsmithing, but that's down the road.