they are both range toys.
The uzi has alot more potential as a SHTF gun, cheaper and plentiful mags, cheap ammo with tons of manufactures. The uzi also has alot of aftermarket parts, and will be alot cheaper to buy the weapon itself. the Uzi is also stupid simply to disassemble. Basically there are only a few parts, and you can have the the bolt out in a few seconds which means a critical jam is much easier to fix.
PS90 is lighter, has a greater range, has alot of the cool factor. its downside is that is high on a possible ban list ( at least the ammo is, and with only one manufacturer of ammo, it makes it a very risky buy), the weapon itself is overly expensive because its made in europe and subject the euro. its alot more complex of a weapon, and hense cleaning is more difficult.