1.  There are a huge amount of alternatives out there for you to choose from.  "Better" is a relative term, and what works for me or a training partner, may not be as effective for you.  You need to answer a few questions before anyone can give you an honest answer.  

a.  What sort of glass are you looking to put on it?  If you are going with cheap glass, or low magnification, it changes some things.  

b.  What sort of ammo do you plan to use?  If you are only going to shoot Wolf, or the cheapest ammo you can find, it once again changes things.  If you are going to have some high end ammo, or reload your own, you are going to want a high quality barrel.

c.  Do you plan on carrying this out in the woods/ mountains/ or other place?  Or is it a bench / range weapon/ or you live in the city.  Barrel thickness can come into play here as part of the overall weight.  


2.  Is your range out in the forests, mountains, plains, desert etc? Or is it a traditional one?  Is it 100 yard and less?  Or are you able to stretch it out to 300 or 600 yards?  


3.  There is a massive amount of information for the new person on the AR15 platform.  This board can be a great resource for much of that info.  However, it is no substitute for real training, and there is also a good amount of less than credible info which gets spouted as gospel truth here. If you are here long enough, you will find guys with tens of thousands of posts who have been here for 5 or more years, who are suddenly looking for advise about what they should buy as their first AR15.  These are the same people which were acting as experts over the years.  Thankfully, there are some highly credible people here as well, with a wealth of technical as well as real world information.  When you read through replies from people to your questions, don't be shy about asking what their background is, or why they are qualified to make the comments they do.  You are spending a good chunk of money on an upper end weapon if you are looking at something even close to a MK12, make sure you get what you want.  Don't let it turn into a disappointment.  


Good luck, and if you run into issues, email Lancelot who is a moderator here.  He is squared away and can help you separate BS from legit info.  

Great update!  Most dealers will have more 16" AR15s in stock, mainly because that is what most people buy.  There is nothing wrong with a 16" barrel, just like there is nothing wrong with an 18" barrel.  Barrel profile will have a lot to do with how the weapon balances for you.  Personally, I would be looking at a medium contour SS barrel if accuracy was high on my list of concerns.  There isn't much reason to go with a fat pipe of a barrel if you are going to actually do things with it aside from plop it on a bench.

You may find that when it comes to a trigger, that you will need to go aftermarket.  Think about whether you want a single stage, or a two stage trigger.  There are people who love each style.  Something else to think about is having a custom build done, which would net you all teh features you like, and avoid you having to replace individual items like triggers.  

The DDM4V7LW is a nice carbine, but I would not confuse that with a precision model.  The largest difference you are going to find is the barrels, which is why Molon (good guy and great source of legit info here) keeps showing you info on barrels.