What's better, 2 leaf or 3 leaf front springs?

[70Chevy4x4Nut]

I have 2 leaf front springs on my 70 4x4. How can I tell if the springs are weakened. They are the negative arch type and when I removed them they lay perfectly straight. Also when I looked in the LMC catalogue I saw that the 3 leaf springs were actually cheaper than the 2 leaf. Which do you guys prefer? If I find that the springs should be replaced, then I may just go with a 2.5" softride lift. I was trying to avoid any more expense right now and so I was leaving it stock height but I don't want to spend time on the old leafs if they are weak.

One more thing. Under each spring assembly there is a small spacer about 1/4" or 3/8" thick. Is this factory or did someone add this in, and I wonder why? It would add very little to the height.

Thanks everyone