Thinking about it, there are probably a few reasons i prefer chapattis:
like your friend. i usually find naans to be more filling leaving less room for the main dish.
chapattis are usually thinner so i find the ratio of bread to meat to be just right in each bite.
flavour doesn't detract from the curry
more malleable and good for scooping *as mentioned).
however i suspect the real reason is that chapattis were what i was introduced to first, as a lad, in restaurants during the early 80s.
Don't get me wrong, i've had plenty of nice naans but given the choice i just prefer the simplicity of flavour and texture of a freshly made chapatti.