The big advantage of a remanufactured engine over used is warranty. Jasper at one time had the best reputation in the industry.
ATK and Proformance also sell reman engines with a good warranty.
I've sold all three over the years, and of the three, only Proformance had a significant comeback rate for failures.
I've installed ATK and Recon (Recon is no longer in business) in a Dodge truck and a Mustang, respectively. Both were trouble-free.
If you're cool with everything being in black spray paint and having a professional install the engine for warranty purposes, a remanufactured isn't a bad way to go, but can be pricey.
For used engines, check car-part.com