I just did all my doors and had the same debate. I ended up doing them by hand for a few reasons, and ran into a couple of unforseen issues that I knew might lurk out there.
The doors I used were 5/32" thicker. All door stops had to come off the jambs as a result. This turned out to be a good thing. All hinges were replaced. The holes are close. also not a bad thing, but picking the hinge-line (because of the slight thickness variation) meant filling and redrilling some holes. This also was a good thing since many of the screw holes were worn.
Method: pull and mark all doors where they came from. Rough cut new slabs to match each one allowing for fitting. Match the top hinge position, rout, and install. Mount the second hinge in the jamb, and then carefully hang the door from the top hinge in the jamb, to mark the lower hinge location. Remove, rout the second hinge and then fit the door. Mount all the hardware, check action and then set the door stops for a solid even close.
The only problem I ran into was the hinges are so free, and the panels are solid (& therefore heavier), that one door wants to close itself. This is because the whole wall and jamb isn't plumb. With the old door and hinge, it didn't matter. I needed to break the jamb free to correct it.
Overall: I'm not a fan of prehung doors unless you're building a room from rough construction and doing the drywall too, or you're doing a big custom entry. I would have bought a hinge guide if I thought it would help me, but sometimes relying on machines and guides causes more work and mistakes.
Hiring someone to do it? You could, but if I did, it would have had to been a contractor tied into the door purchase like you get at Home Depot, so I had leverage on the workmanship. I saw their advertised rate, but that was for a prehung unit which meant new moulding and possibly drywall, not to mention inconvenience. Either that or a higher rate for the custom fitting. I'd go the route I did, if I did it again. You have to have an electric planer if you do though. Also... it will take more time than you think.