Coir

Pros: Coir, a coarse fiber that comes from the husk of the coconut, is a plentiful and renewable resource. It is absorbent, and its texture makes scraping shoes easy. Widely available. Biodegradable.
Cons: Can shed excessively. Expands slightly when wet and shrinks slightly when dry. Not easily cleaned. Shortest life span.

Rubber

Pros: Resilient and long lasting. Inexpensive. Easy to clean.
Cons: Smooth underside can be slippery when wet. Not biodegradable, though you can find mats made of recycled rubber.

Polypropylene Rope

Pros: Reversible. Won't rip, rot, or fray. Easy to clean with a hose. Inexpensive.
Cons: For use on non-slip surfaces only. Not biodegradable.

Zinc or Cast Iron

Pros: Ideal for heavy-duty wiping, scraping, draining. Won't peel or rust (though the color may darken over time). Easy to clean.
Cons: Usually more expensive than rubber or coir; comparable in price to wood. Can get hot in the sun.

Teak or Cedar

Pros: Resilient to the elements, since these woods contain oils that prevent drying, cracking, and rotting. Slatted designs channel away dirt and mud.
Cons: The world's wild teak population is being depleted; plantation teak is less durable. Cedar, which is not endangered, is not as durable. Teak is more expensive.