It depends on what you are mining, and your cost modeling. For instance, NVIDIA cards have better memory bandwidth and both dagger-hashimoto and equihash are memory hard algorithms, and NVIDIA cards have better expected resale value (though this will vary based on your expected sales channel.)

AMD is generally more popular among hobbyist miners, I think, because early on they had a performance advantage in Ethereum and hobbyists tend to follow each other like a herd because they have limited time to do experimentation and exploration (and this is not a criticism of them, they have day jobs and it takes a lot of effort to even get miners going, let alone optimize them across multiple parameters.)

I thought they use AMD cards because they consume less power