Have you noticed a significant drop in performance/mileage? IF so, check your fuel pressure to make sure it's within spec. If you're running overly rich for an extended period of time, it will destroy your catalytic converters. So, make sure the fuel system is healthy before you replace them otherwise you'll be doing it again in short order. Also, hook a scanner up and look at your ECT temps to make sure your ECT sensor is functioning properly. If that sensor is bad, it will dump fuel, again destroying your catalytic converters.
Magnaflow converters are a nice replacement, especially if you still have the stock exhaust system. If you're not stock, consider the high flow ones. They work well to.
If you're replacing the O2 sensors, DO NOT BUY BOSCH OXYGEN SENSORS!!!!! Go Delphi/Delco. Rockauto.com usually has the best prices. DO NOT BUY BOSCH OXYGEN SENSORS!!!!!