Venomous or not, both species bites, so you'd get gnawed on one way or another. That said, snake bites would hurt more, but spiders can crawl into your ears and up your nose; so on. Honestly, just because of that part, I think I'd go with snakes. I can deal with bleeding and a few scars better than I can the thought of something nesting in my ears. Not afraid of either one, but it's still scary to think of Charlotte being a turbo bitch and building her web in one of my facial orifices. Dnw.

I could totally chill with a bunch of mantises. I would be mildly creeped out, but if I left them alone then they would leave me alone and perhaps I could study their ways of communicating, which could be handy when the invasion comes...