Q: Which is better to have strong muscles or muscles that are hard to the touch?

A: It's each individual's choice what aspects of physique appeal to them, so it's impossible to answer which is 'better'. However I want to note that the actual hardness of the muscles does not change with training, only muscle size and strength do. What you are probably talking about is how the muscles of people with low body fat feel harder than of those with higher body fat -- that happens not because one muscle is harder than the other (as I said before, actual muscle's hardness is about the same for everyone) but because the person with low-body fat has less flabby fat covering the muscle, making it appear harder.

Of course, it's perfectly possible and normal to have both the low body fat and strong muscles -- the same weight training that makes your muscles strong also helps you burn fat leading to low body fat. So you can have the best of both worlds!