If you are connecting with GO or VIA at Union Station (or the Porter shuttle), the UPE will also be excellent. And, in general, the chances of getting caught in traffic in a cab or encountering various cab-borne discomforts makes the UPE attractive. If you compare the cab fare, don't forget the customary tip in your calculations. I will be glad to use the train. The TTC subway and bus at rush hour especially are not a place to be hauling luggage. Since the trip to Pearson is not a daily occurrence the higher fare is not as big a deal as it will be for those work at Pearson.