Re: new ar-15...what sight should i get
On 14.5 barreled carbine I use a 4 X Trij w/bdc and piggyback red dot for intermediate range and groups, and Eotech for Run N'Gun. Although the mini dot works on the Trij, I don't like changing my weld and loss of sight picture when transitioning between the magnified optic and the dot. Eotech Gets +1 also if you have, or intend to use NV at any point. As others have suggested, it's best to determine what your doing with the rifle, and then match optics. Just my two pennies.
Best of luck!