When looking at a single solar charge controller versus three, you also have to take into account the cost of additional wiring, additional fusing (for 2s3p) and time to install. In my case, I simply didn't have room for a third solar charge controller.
3s2p is the least expensive and easiest way to install. It still has some coverage for shade.
Given the cost difference, if I had the room I would probably go with the three 100/30 and not carry a spare. Like you said, if one craps out you've lost only 1/3rd of your production. A quick install of a Y connector could remedy that. But I haven't run the numbers to see if 2s2p will fit a 100/30.
3s2p is the least expensive and easiest way to install. It still has some coverage for shade.
Given the cost difference, if I had the room I would probably go with the three 100/30 and not carry a spare. Like you said, if one craps out you've lost only 1/3rd of your production. A quick install of a Y connector could remedy that. But I haven't run the numbers to see if 2s2p will fit a 100/30.