The JT9s have the reputation of being very easy to maintain
These things are the worst ever to work on. You try getting the reverser fwd after it's got stuck in full reverse, operate the 3 way valve, can't do that as you need to open the cowl, which you can't do as the reverser is out
If you do manage to get the cowls open try closing them again!
Having worked on (rather still working on) all 3 I'd say the RR, then the CF6 then the Pratt for ease of maintenance.