Dear Alias Azher.
An X potency is diluted on a 1:9 scale -1 part remedy to 9 parts liquid or solid. A C potency is diluted on a scale of 1:99 -1 part remedy to 99 parts liquid or solid. Therefore, a C potency, by being more dilute, may be considered “stronger” homeopathically. However, stronger is not always better. If you wanted a 30c but can only get a 30x, the 30x would be fine because both have been diluted 30 times. It is the correct remedy, not the potency, that makes the difference.