Now that you know the similarities and differences between butter and cream, if you think there will be a difference in your muscle-building results, try one for about 6 weeks, then the other for about 6 weeks... or whatever amount of time you choose. Your choice might also be based on which one fits into your eating style. Or you might like variety, so get some milk fat from cream and some from butter.
Also, amounts of protein and carbs play heavily in muscle building. If you set your protein level and daily calories to your activity level, you can play around with the fat/carb ratio and see which works the best for you. You really can't guarantee results with somebody else's ideas - that's why you can get conflicting advice if you look around at what others are doing. Read up, but the final answer is what works for you.
Finally, a lot also depends on your body composition and metabolism. For example, I know two brothers, and one of them effortlessly maintains about 11% body fat no matter what he eats, while the other has to be very particular about his meals in order to stay strong and lean and still never gets under 18% body fat.