Our cat would get so stressed when I tried to put her in a carrier that she would attack me. I still have a scar on my left arm where she bit me hard enough to sink her canine teeth all the way in. I had to cancel the vet appointment that day because I was bleeding profusely and the cat was hiding somewhere in the house.

After that I bought a soft carrier, too. Mine is called "Cat in the Bag" or something like that. It's literally a canvas sack with a zipper, a carry strap, and a head hole with velcro adjustment. I just pop it over her head, adjust it to fit, then zip her up. She's contained but her head is out and she can look around freely. She still doesn't like it, but she doesn't freak out and go into fight mode.