Everything except the bellhousing bolt pattern is different. Of course one is better than the other but it depends what area of the engine you're talking about.

Front distributor (Buick) is better for less spark scatter but worse for cold starts and oil pressure because of the long internal passages. Bore to stroke ratio and rod material - forged - is better on the Buick, thin wall casting (Buick) is lighter and has a higher tin content so it lasts longer but can only take one overbore, the mains will exit out the bottom as you pass 575 ft lbs of torque unless you have a bottom end girdle (Buick) - and so on.

I have run several Buick 455's and they are easy to make power with. However, you won't find one in my Firebird - ever!

The Buick engine is a good engine but has its problem areas, same as just about any engine out there.