all depends on what has been/needs to be changed out really, and how bad you want it. i would say, based on experience, buying a truck that has 150,000 is probably better than 50,000, because nothing has been replaced on the lesser miles truck, whereas the truck with high mileage probably has had some new parts thrown on there and is ready for another 100k mile run around.
i bought my truck with 63k, and at about 80k i needed to do ball joints, had to replace the torque converter, had an alternator at 100k, had a vac pump, and a starter. if somebody buys my truck today with 187k, they get all new stuff! just something to keep in mind.
if you do a search, there are a few threads on what to look for when buying a used OBS.
WELCOME to the forum, and good luck with your shopping!