If you have already done some fasting and your goal is minimal muscle loss, I would highly recommend water only. Water only will maintain the strongest state of ketosis and ketosis is what turns on your fat burning hormones/enzymes. Juice and even low calorie diet drinks can trick your body into a transitional state of ketosis. That transitional state is when the highest amount of muscle loss occurs. It doesn't matter which type of fasting you do, muscle loss will occur. The difference is how much. The longer you stay in a state of ketosis, the close you will get to a 90% fat/muscle loss ratio. If you do not maintain a strong state of ketosis, the ratio is closer to 50%. Water Fasting imo is not harder than juice fasting because you do not "tease" your body into thinking it will get food. After a few days, I think the detox symptoms are similar so stick it out for about 3-4 days on water and I think you'll be better off for your particular goals.