IMO a tarantula is eaiser to take care of. A emperor scorpion needs a deep enough substrate to burrow (you might not see it much). A heat mat and you got to keep your humidity up without letting the tank get moldy.
Tarantulas on the other hand, stay at room temperature (most of them). If the temperature gets real low you would need a heat mat. And if you get a terristerial tarantula they wont burrow and stay out in the open most of the time. With tarantula's a lot of the pretty mexican species kick hairs so you would have to consider that. This was a real quick reply so if somone has something to add or whatever please feel free...
This should help you out with picking a tarantula (plus other things):http://www.arachnoboards.com/ab/showthread.php?t=55206