I've always gone with the 4" x 0.75" all plastic caster for lighter weight and lesser resistance. The draw back is that they tend to lock up on items as small as a pebble and they tend to pick up and twist fabric in between the hub and fork. I am thinking of changing to the 4" x 1.4" aluminum rim and plastic tire caster. The Aluminum is more durable and looks better. The wider tire should roll over stuff that the narrower tires lock up or pick up. Any experience with these? I don't want the extra weight if it doesn't buy me anything more than bling.