I normally get into AR10 vs. M14 Discussions at least 3 times a year. I guess it's a slow year? Anyways, AR10 all day long.
As a HOBBYIST AMONG OPERATORS, here is my Hobbyist view of things.
1) AR10's come with a Scope mount included:
This is huge! A quality scope mount on a M14 will cost you about $200, and even if you do get a mount, they come loose quite often. A M14 receiver tries to twist it off. AR10, the mount can't come loose (because it's part of the upper receiver). Another problem you will find with a scoped M14 is cheekweld, actually it's more of a shoulderweld.
2) Bolt swap on an AR10 is easy:
On an AR10, just crack her open and put in the new bolt. With M14's, a bolt swap is a complicated process. Once you put in your new M14bolt, you have to lap the bolt and time the barrel to get that "magic headspace". If you have a Smith do it, he will charge you a pretty penny.
3) Barrel Swap is easy on AR10:
With an AR10, all you do is unscrew the old barrel, and screw in new barrel. No magic headspace needed. The barrels come pre-headspace from the factory. With M1A's, you have to find the "magic headspace" after you install a new barrel by timing the barrel and lapping the bolt.
4) Better Parts availability for AR10:
You can get everything for an AR10 directly from the manufacturer if you have to. With M14's, parts are not evn available from the Mfgr, and on top of that, surplus USGI parts are not really easily available anymore. Extractors, bolts, BCG, buffers, are easy to get for the AR10.
5) Better Aftermarket accessories for AR10:
For AR10s. the choices for triggers, stocks, and forends is endless. How about a nice trick barrel for an AR10? Yep, your choice. Noveske, White Oak, Schillen, etc, and you can install the barrel yourself without trying to figure out the magic headspace. Also, try getting a nice trigger for an M1A, tell me how that works out for you.
6) AR10 has the better chassis:
Reason AR10 has a better chassis is because it does not have one! It has an upper and lower, and with the correct forend/rails, you can easily FF the barrel assembly. A quality Chassis for the M1A will run you about $700.
7) AR10's are inherently more accurate:
AR style locking lugs and naturally FF barrel, you will find that it takes a lot less work to make an AR10 accurate.
8) AR10's are easy to Smith:
You can do everything on the AR10 yourself. Bolt swap, barrel swap, extractor swap, etc. No "magic headspace needed". If an AR10 does go down, they are easy to get back up. Lots of little parts on the M14 that can fail, and when they do, it's not easy to replace them and get the gun working again. Both the M14 and AR10 are fairly reliable, but what makes the AR10 10 times better than a M14 is that you easily get it up and running easier when it does break.
9) AR10's can handle hot rounds better
Hot rounds are not a problem with the AR10, the AR10 laughs at hot rounds. With M14, all it takes one hot round and say hello to Mr. Bent Oprod. A bent oprod on a M14 will turn your M14 into a club. USGI Oprods for M14's are no longer available, and even the cheap ones go for about $200. M118LR was actually loaded lighter because all the combat M14's were getting beat up.
10) AR10's does not beat up brass as much as an M14. The AR10 can get about 10 reloads from one case (LC case). The M14 beats up brass so much that you would be lucky to get 5 reloads. #10 is really for reloaders only. I know all you Operators are too busy training and do not have to reload.
11) AR10's look better.
This should be #1. Looks matter! Looks are everything.
The Cartmann .308 Family: