In 2007, I lived a few months someplace with a dishwasher that was 100% under my control. I don't think I tried EVERY detergent, but I do know every time I bought a detergent, I got a different brand type. My memory is hazy, but I don't recall being unhappy with anything. I suppose when I have a dishwasher again, it will likely be more of the same: something new each time, unless there is some compelling reason to lock into a particular brand.
I do have a couple of biases. First, I like powders, although that is less about perceived real world benefits and more about it's what I'm used to. A pod of some sort is probably more convenient, but I don't mind filling the little detergent cup.
I also have a warm, fuzzy spot for Cascade...but that's only because that was the brand I remember from growing up. We had, but almost never used, a dishwasher, and Cascade was the brand of detergent my mother used.
I wonder about scents, too. Part of me likes the idea of unscented (Seventh Generation had a powder like that). One thing I don't want is dishes with a scent. But IIRC the scent can at least add a perfumey aura around the running dishwasher.