I always do it in a Crock Pot - through them in on low, dump in lots of marinade (Italian dressing or whatever), and let it cook. Dumping a bottle of beer in with some breasts makes great chicken for sandwiches!
This is easy and very good. The marinade/seasoning is perfect for eating straight or on sandwiches/salads. It has flavor but the flavors aren't overwhelming so they play nicely with most dressings, sauces, etc.
The key is to pound breasts out to an even thickness so they don't have to cook as long. When I do that they aren't dry, and they only need to cook for a few minutes per side.
I bought a thermometer and it helps cook chicken TONS. No more dry chicken because it beeps when the chicken hits 165.
I like to either cook the chicken breasts in chicken stock in the crock pot or using the oven and putting a layer of parchment over the chicken so that the juices stay trapped.
My very favorite juicy chicken is on the smoker. It turns out so good every time. My h seasons it with seasoned salt or we marinate it in a combo of an acid, an oil, and seasonings, depending on what we're in the mood for. I love vinegar, so it's often balsamic vinegar and seasonings.
Becker chicken marinade is fantastic My favorite way is to pound thin, season with salt and pepper. Heat some butter in a pan, sear on both sides. Finish in a 425 degree oven until cooked through.