Sorry, but if what you listed are the major concerns and you want to fly 5 pax or less there is 1 helicopter that thrives in those circumstances with lots of power to spare and in my experience extremely reliable in hot and high and humid conditions-AS350B3+
. Hot and high she out performs most light twins on payload(real hot and high). She has only 1 engine but comes from a family that has accumulated over 20 mil hours that has to be taken in to account when we talk reliability and most of those hours in the worse places you can think off. If your friend wants a twin, look carefully at the OGE graphs and remember no use you look at both engines operitive otherwise you are flying a single for all practical purposes. One also, as mentioned before, can not just talk of 109 or 135. Their performance vary big time between the variants. As mentioned with the 109, you can not compare a 135 with a 135N2/P2.