I do not think there is a lot to choose between the two types of gasket, but I have used the one piece one. But I would not use both!
I am guessing that both were used because the gasket set included both, so the person fitting it thought they should both be used. 
The secret to success in installing the manifolds is to gradually tighten both the studs into the head and the studs holding the two manifolds together so that neither is holding the other out of alignment. start by tightening the nuts holding the two manifolds together just enough to take up the slack, but still allow them to move, then bolt to the head, but again leaving the nuts loose enough to allow slight movement, then tighten the first set a bit more, then back to the second lot, and finally torque them.
John
				
			 
			
		 
			
				
			
			
				John
JDNSW
1986 110 County 3.9 diesel
1970 2a 109 2.25 petrol
			
			
		 
	
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