IMO, in a older (pre-1995) GM engine, you should choose the ACDelco spark plug heat range recommended by the auto manufacturer but convert the ACDelco heat range to a another brand. I quit using the fake ACDelco Rapidfire #1 spark plugs and installed Denso PTF16TT platinum spark plugs. The Denso PTF16TT spark plugs have a similar heat range as the ACDelco RapidFire #2 platinum and ACDelco R45TS copper spark plugs. I used the Denso PTF16TT spark plugs but I felt that they were too hot, even for stop and go driving, because they were pure white when I checked them after the first 4,000 miles after the engine rebuild. I switched to Denso PTF20TT which the step colder. I have not checked those yet. My TBI engine seems to be running lean after the engine rebuild so that may be why the plugs were pure white after 4,000 miles.
Worn out engines, highly modified engines (such as mine) and engines used in the higher echelons of racing require the plugs to be checked and replaced more often.
I prefer platinum fine wire center electrode spark plugs because I want to change spark plugs as few times as possible in a congested engine compartment. I expect the Denso PTF20TT platinum spark plugs would last for 60,000 miles in a good engine but I will change them at 20,000 miles whether they need it or not. Another feature I like about Denso PTF20TT platinum/titanium tip spark plugs is the price...$3.00 each including shipping.