I have a love/hate relationship with spiders. They fascinate me and totally creep me out at the same time! I really like the garden spiders around the house and yard (as long as I don't walk into their webs), and some of the larger ones have very cool markings. But the hairy, knuckly ones that skitter around the inside of the house - those, I can do without.
So in D&D, I would pick spiders as my favorite animal/vermin. For DMs, they are incredibly versatile - they come in sizes ranging from tiny to big as a frickin' house, web-spinners to hunters, and can go up against characters from first to epic levels. Just keep them out of my sight.