Tamiya made a kit of the Merk Mk. I which is okay if you can find it. It came out when the tank was brand new. Academy has a decent Mk. II. Avoid the Mk. III by academy as it is a bad kit of the prototype tank and does not build into anything like the actual production vehicle. Academy just put out a decent Mk. IV... Legend of Korea has a lot of upgrades for all of the various kits if you are into super detailing or want to make a good kit better.
The newish Dragon Abrams tanks are quite good. Tamiya's current issue of the Abrams is also very nice and builds very easily, something that Dragon kits sometimes do not do well... Avoid the Academy Abrams. Itaerli's is so so but some issues are sold with an interior if that is of interest. When you say M-1 I assume you mean the Abrams in general as the current versions are the M1A1 or M1A2. If you have to have the original 1970s vintage M1, Tamiya made it many many years back.
I built the dragon M-1 when it first came out..I got it for the interior.
It was a fussy kit but it looked ok when finished. I also built the italeri M-1 (pretty basic). I had the academy Merkava but gave it away...I liked the seperate vinyl road wheels and the nice machine guns
The first Tamiya M-1 Abrams was released in 1982. On the cover of the box it shows a version that belonged to 1st Armor Training Brigade, Charlie Company Fort Knox, Kentucky. The " bumper numbers " on the tank are AC 1BG / 1C13. The commander in the tank was Staff Sergeant Jim Bias. He was one of my drill sergeants when I did my Basic Training in the summer of 1984, and I was assigned to that very tank on the box.
The Academy versions of the Abrams releases are copies of the Tamiya releases. The molds are identical. They cost a little less.
I favor the Tamiya kits. They do build easy and look great when completed. I built the Merkava kit from Tamiya and like it. As far as what the best kits are, everyone has an opinion. But I think you cant go wrong with Tamiya.