ok.. if your looking for power and you want to do some head work and bore out the pistons stuff like that , then having the motor rebuilt would be the way to do it because someone can make those changes while rebuilding the block.. but that costs money and isn't cheap.. now the remanufactured engine depending on who you get it from is more or less the same thing but they remanufacture it to the factory specs, meaning it's going to be the same power as it did when the car was running with a factory motor , but they do give some type of warranty which is a good thing, check out jasper engines, a bit pricey but there solid motors.. it's simple there is more of a chance of internal engine failure from human error when rebuilding, and less when remanufacturing because allot is done with machines and to be honest i would go with the remanufactured motor , just because the company does it all day every day, verses someone manually rebuilding a motor from time to time... but the question is are you just looking to get your car running as it should or are you looking to juice up your car to make it faster.. i just hope there is a reason you have to replace the motor , and your just not trying to make it faster. also depending on what kind of car , you can always just swap a bigger motor in the car which will give you more power..