An M4 is still an AR-15. They are all AR-15's.
I think what you ment was you dont want an A2.
I know it can get confusing, and I think your best bet is to visit a local gun store and not a big chain outfit. If you want a scope, get one without a front sight. Most with the front sight, that sight doubles as the gas block, as there is a hole in the barrel there and it goes through the sight and down the gas tube to operate the action. So removing the sight, it would need replaced with a gas block.
I am not sold on "colt is the best". IMO, colt is only best at holding resale value. Dollar for dollar, you dont get more with colt, I think you get less because you are paying for the name.
Not picking on anyone or trying to start a war, but compare a deere to a kioti. Both make a fine piece of equipment with excellent quality. But feature for feature, one cost more. IMO, that is just like comparing colt to about anything else.
Apples to apples, colt is going to be more $$$.
Colt does not make a low-dollar AR. All of theirs have the things like dust cover, forward assist, and chromed barrel as standard.
So when looking at another brand, dont look at the entry level $600 guns, rather look at one that compares feature for feature. The colt LE6920 is typically $900-$1000 range. Many other brands with the same desirable features will be ~$750-800.
There are so many options out there to compare, and its hard to go wrong with any of them. Again, I would start by seeing what you have available locally. It could be easy for me to recommend a particular model of armalite, bushmaster, core 15, CMMG, rock river, windham, ruger, S&W, etc. But it would do no good if your dealers arent distributors. Unless you plan on buying one online and paying FFL transfer, which is a valid option as well.