Forgive me if my eyes deceive me but no has mentioned the BIG advantage of less yaw during engine out ops?
With pods close together (laterally) down the rear any yaw induced due to e.g. a V1 cut, will be markedly reduced compared to a underlsung-out-on-the-wing jobby.
Mucho Advantago!! Less yaw = less rudder required/introduced to airflow = less drag on the single engine.
Also (I minor Geekee point):
The T-tail by its nature will 'end-cap' or 'fence' off the end of the fin. By doing so it limits any tip vortices/marginal spanwise flow and improves the effectivness of a fin of a given length thus allowing a slightly shorter fin. There is also potential for an improvement to induced drag = fuel saving. So much so that Boeing toyed with the idea for the 757 to have a T-tail config with its current underslungs....but it must have looked stupid and I guess that old phrase 'looks right - flies right' got the better of them.
This is however only derived benefit and perhaps not a true 'driver' for the confirguration in the first place. In fact it is only by moving the engines from the wing that 'forces' the desginers to move the stabiliser in the first place.
From what I've read on the subject the T-tail rear engined designed aircraft all had the following Primary Design Driver in common:
They were all intended for regional/rough strip/commuter or high frequency ops with the minimum of infrastucture at airports driving the following:
>They needed to be self supporting(DC9/BAC1-11/F28),i.e. airstairs, low hand loaded baggage holds - short turnarounds which meant they had to be LOW to the ground = too little clearance for a traditional underslung engine design - not without forcing the engines to become part-time sandblasters. And if you can't put the engines under the wing and you have to put them on the rear fuselage...then where do you put the stabiliser?....on top of the fin......
>Also whilst operating from little used/'Empire' strips/commuter towns it made sense to mount the engines so that they would be effectively shielded (in part) by the main plane from FOD/gravel. This also conveniently then made them prone to ingesting less than silky smooth air from the wing which was an undesired consequence but they try to iron it out with more carefull geometry on subsequent designs. (altough the MD-80s used to munch down fuel Ice off the wings with alarming frequency in a certain air-touring airline I believe).
Even the Biz jets of today seem to be driven by this need to be low to the ground which then drives the rest of the configuration. Perhaps its not so much the case of advantages or disadvantages because in many ways t-tail rear engine is a pain in the arse......its more a point of what they need the aircraft to do and be good at.
Thats my take on it....but as for the VC-10...I think it was the pursuit of beauty that scultped it that way!
Final Geek-fact - the original EMB145RJ design was an t-tail but with the engines mounted ABOVE the wing in pods and that did look stupid.