My experience with water pumps is that rebuilt pumps are not worth the powder it would take to blow them apart. Six months is all I could ever get out of a rebuilt. When I have gone new at twice the price, they have outlasted the vehicles.
That said, you have gone both ways, so either you got real unlucky with your new one, or there is some other unknown problem. I would go with another new one. If it pukes again in short order, then I would have to assume that something else is causing the problem as I would find it hard to believe that two new pumps in a row would be the same quality as a rebuilt one.