I have a DPMS LR 308B that has been totally reliable, never a failure of any sort, it is very accurate, consistently sub moa with decent ammo. Mags are $28.00 each on gunbroker. It will fire safely almost any commercial or military surplus ammo. Earlier designs from other manufacturers did have functioning problems, mostly with magazines.
The m14, (and it's forefather the M1 Garand) while a fine battle rifle, should not be fed many types of commercial ammo or used with the slow burning gunpowders generally employed with heavier bullets. They can be modified to use these bullets & be extremely accurate but at significant expense. They are also notoriously hard on brass. Two or three reloadings is all you normally get from your brass.
Accessories are less common and expensive when compared to an AR type rifle, particularly optics and optic mounts. (however the battle sights on an M14 are excellent)
Something to remember, that the M1 / M14 designs are almost 80 years old while the AR series is perhaps 40.
Finally, the M14s of today are made of parts coming from all over the world including China with attendant quality questions. The days of Springfield assembling their m14s from surplus GI parts are long gone.
In the end, you should actually buy one of each. An M1, an M14 and an LR 308, you can then enjoy life!
Roger