Without doubt, the 3.0 is the peach of the Omega engines. The 3.2 is less powerful in reality and a damn sight more thirsty.
The (poorly mapped) DBW throttle of the 3.2 makes it seem more sprightly when pootling about, but thats because it artificially opens the throttle a lot more than expected on pull away. Bury the throttle on either from a standing start, the 3.0l is the one to have. Also, with a mechanical throttle, if you do bury the throttle and dump the clutch, the 3.0 is easier to regain traction, as the DBW needs more guesswork (though consistent, so easy to master)
The 3.2 is hampered by the cost cutting exercises, including the removal of the EGR, which means the compression ratio had to be lowered, and then the cc increased to give similar power. The compression ratio kills it.
The same story goes for 2.5 v 2.6.
I owned both (autos) side by side for several years, and I've driven more Omegas than I care to remember (hundreds) of all engines and boxes.
I have to add, I particularly detest the Omega manual box due to its throw. But for outright performance, 3.0l manual out of the standard options available.
Anyone trying to make out that the 3.2l is better in any regard over the 3.0l hasn't driven many 3,0l ones.