I have 2 to choose from
one FN Herstal and one Utah assembled in Portugal

will be sending off to NightHawk for slide to frame fit, match grade trigger job with all new components,
Complete Action tune package, Barrel fitting of a new threaded Alpha Wolf barrel
happy with current sights; Heinie on the Utah gun and some kind of factory site on the FN that are larger than original. easy enough to see but
not as snag free.. if the FN is the one to do, I may have the Hienie front and rear installed..
they will stipple front strap and back strap and then a Cerakote finish on the complete gun.

I am leaning towards the Utah gun, have carried it for 20 years off and on with a Colt Commander (Which may be going to Wilson or NightHawk)
it is smooth as melted butter as far as you'd consider a "melt job" and think it will refinish nicel.
the FN is a newish police trade in from Israel i picked up a couple of years ago when the market flooded
I have sub $350 each in the guns...

lookin at at about $1600 to $1700 in the package..
the remaing will go in the safe for future generations
I am assembling a set of "heritage guns" and dumping the meh weapons into the market in November...

If the one is like melted butter I'd keep it that way and do the other.

FN.  I have a Yost gun with "Assembled in Portugal" on it and to be honest, it really bothers me.

The FN, never liked the "Assembled in Portugal" either.

Cast or Forged frame?

Mark III?

My understanding is that the cast frame is newer/better for customization.

The Utah gun if it is half as nice as you say.  Plus, it is an old friend, it has earned it.
Portugal never bothered me a bit.

Both are steel framed guns

Yes, both are steel.

However, newer HP frames were cast while older frames were forged.

Difference

trust me these are not "newer" guns

+1

Don't let it bug you.  There's a bazillion AIP Hi-Powers out there and they run just fine.  The only thing you "need" to change is likely the sear but only if you shoot it heavily.

Curious why you chose Nighthawk for the custom work, shorter turn around ?

All BHPs since the late 70s have been assembled in Portugal no matter what the slide says.