Snakes such as rattles let you know when you irritate them by shaking their tails. Spiders such as the black widow will just straight creep up on your ass without you knowing.
I used to own a snake but it died because I forgot about it in the garage. Spiders are cool, like when they run I like to look at all of their legs move fast.. If I had to choose one, id say snake cuz the anaconda can get long as a bus I heard.