How does an Airbus pilot decide whether to use HDG-V/S or TRK/FPA guidance? The Flight Control Unit of modern Airbus aircraft has a pushbutton for selection of either 


heading / vertical speed (HDG-V/S), or
track / flight path angle (TRK-FPA) 


guidance for the Autopilot and Flight Director. I know in principle what these modes mean (i.e. difference of heading vs. track, or between vertical speed and flight path angle) and how the guidance on the Primary Flight Display changes from Pitch/Roll bars to the Flight Path Vector depending on the selected mode:



What I would like to ask is when is each mode used. How do pilots decide which guidance mode suits them most in a given situation? For example, is it related to


personal preference of the Pilot Flying?
specific flight phases or situation/circumstances?
procedures that require a certain selection?
It's mostly up to points 2 and 3 on your list rather than personal preference:
Note that most ATC instructions (beit on departure,cruise or initial approach) will ask of you to fly a specific heading and/or a specific climb rate (v/s). This makes the hdg/vs mode the 'standard' mode to be used durring flight. This is also the mode where the F/Ds provide an easy to use guidance for the pilots to follow.
The reason for this Hdg preference for ATC is beyond the scope of this question, and is quite a nice narative on how historically we arrived at using heading for separation, but I will say this much: imagine ATC software attempting to interpolate the track of two converging a/c , to determine minimum separation and/or collision conflicts. Now imagine there is (unkown to the atc) changing wind along route, and both a/c will change hdg to maintain proper ground track. The math required is mind-blowingly complicated...(because changing hdg will change time of arrival at intersection,etc )
Anyway, once you look at some final approaches you will see that there is usually a final approach Track and a (3deg usually) glide path angle posted on the chart. The reason is that being closer to the runway, you start to become a bit more interested in your path wrt to ground rather that wrt to other trafic.
TLDR
TRK-FPA, as part of normal operating procedures, is only used when flying the final part of a non-precision approach, and is usually engaged  about 1 NM before the FAF.
Mind you, it's use is not prohibited outside of that, just there is kinda little use for it.