Novelty dog beds can be comfortable if they have sufficient padding that holds up to wear and tear. It also helps if they have a padded wall around the edge for the dog to lay against.
High-quality padding options include memory foam, orthopedic foam, and dense polypropylene fiber. Avoid lightweight polyester padding, especially for large dogs who are heavy enough to completely compress the padding.
Novelty dog beds sometimes forgo high-quality padding in favor of more design-focused materials rather than practical, but this varies widely. Look at user reviews and see if any of them review the long-term durability of the bed.