Depending on which of the three mounts are bad; I'd say stick to OEM for the passenger side and driver side mount but would suggest going to a stiffer mount for the dogbone/transmission mount. The passenger side is usually the one that goes bad, second to the dogbone. Replacing the dogbone with a stiffer mount may increase vibrations some but i feel the benefits from it being stiffer (especially the feel with manual trans) outweigh the slightly increased vibrations. Non-OEM replacement mounts have a bad rep of failing prematurely, from what I have read.
For aftermarket mounts check out Central Florida Motorsports
, they will have more of a selection on poly mounts (as well as oem.)
For OEM, I suggest giving Steve at Tousley ford a call. They give us a deal on oem parts.
phone: 1-800-328-9552 (ask for Steve in the parts department)
Order online: http://www.tousleyfordparts.com/