Are both sentences below grammatically correct, and are they both used equally in conversation?
Stacked adjective: あそこの奇麗な面白い人は、誰？
Non-stacked adjectives: あそこの奇麗で面白い人は、誰？
From what I've seen in even the easier-to-read newspapers and heard in various shows, it is allowable to stack adjectives like that. Although, the case may be that they are more colloquial.
Also, there are two ways to go about I-adjectives:
The second case is a mid form of ～くて and is frequently found in writing.