I don't think you can meaningfully say that LatLong OR UTM are "accurate" ... they are simply measuring systems and artificial ones at that. UTM, though, has a granularity of one meter, you can't measure anything closer than that, LatLong, though, can position a spot to as close as however many decimal places you want to waste.
So, using UTM you can get within one meter of whatever you are describing, with LatLong to however close you want. But what's practical? My GPSr claims 7 foot accuracy occasionally. Do I believe it? No. But even at that claimed accuracy it still can't get me beyond UTM's granularity.
So, what am I saying? Use what works for you when you need it. Luckily the newer (and maye older, I don't know) can convert seamlessly from one to the other, and because the conversion is only as accurate as the current fix, they are EQUALLY accurate.
YMMV
Bill W