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I'd say easiest from underneath ; water pump is in the lower 1/2 of the front of the engine.
Remove serpentine belt and tensioner , for best access.
Having said that ; reinstalling the serpentine belt may require access from both top and bottom .
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.