Bear in mind that cheap foam wears out quickly, while good foam, though expensive, is durable. Unfortunately, it's hard to judge foam by just looking at it. Crash pad bells and whistles are a personal matter. Carpet or fleece covers are good for wiping feet on and may keep the pad from sliding on moderate inclines when flipped upside down. Zippered accessory pockets are a fine touch that could save you from losing your keys or wallet.
Some pads have flaps to prevent gear, loose inside, from falling out.
You may want to check to see if the fabrics are waterproof, or for some water protection of open-cell foam within the pad. One of the biggest factors to consider is durability.