The mummy is a great indoor thrill ride. There are some great visual effects as well as cool motion elements.
I've been on both, and the backwards part in Everest almost gets me nautious depending on where I'm sitting in the train. There is not really any spot in Mummy that kicks my motion sickness in.
Everest is much longer than Mummy, but Mummy offers more of a story feel to it.
Both rides are great IMO and if you can handle Everest, Mummy will be fine, and fun.