Regular servicing seems to be key, so go for the one with the best service history. 15p engines were later than the 10p units so would have ironed out alot of the problems. Generally seem to be a strong motor with heaps of potential.
A stage 1 tune helped me to iron out the flat spot on low revs when pulling away. If I was to tune further on my 10p I would need to check for nylon dowels under the head, but it's done 110, 000 so far without too much going wrong.
As Discomania said: injector loom; fuel pressure regulator; and I have had a new water pump and starter motor. All DIY so relatively easy to work on.