It is highly arrogant to believe that A&M is hated the most. A&M is pretty much an afterthought when others mention texas schools.
If you are referring to the Big XII schools in Texas, they might all point to A&M as their least favorite of their Texas brethren. But that is because tech and baylor are merely pests to tu, and tech and baylor feel like they aren't in the same league with tu so they focus on A&M.
However, t-shirt fans only care about OU. And I have only heard respectable things coming from non-tshirt fans when I say I am an Aggie. Fans from other universities (Tech and Baylor excluded) will talk to an Aggie before looking at anyone in burnt orange. I got high fives from Sooners for wearing maroon at the Red River Shootout, I've had free food and beer from Okie Cowboys, any fan from the SEC will smile, nod, and say "**** Texas" to an Aggie.
Students from schools like Rice, TCU, North Texas, Texas State, show more attention to tu than A&M because of the multitude of tshirt fans. SMU fans show more animosity to A&M over tu, but they say it is because they preferred the rivalry between our schools than dealing with tu.