There's quite a size difference there.
If all your characters are going to be that size it would probably be easier to shrink the rig to fit so that its interchangeable with other small models. ( You'll probly need to make bone diameter smaller as well. (?))
But, generally, it would probably be easier to scale the model up to nearer the size of the rig and just tweek things a bit when it's close.
EDIT: The thing to keep in mind would be the sizes of other models and props that you have, or intend to have. I'm not really sure if the gym rig is abnormally large, tho i don't think so. ?
If you try shrinking the rig, and find that you do need to make the bone 'diameters' smaller, then it's likely that the model is quite 'small' for anim8or, and i would go for a model that suits bones with a diameter of 1. (default)
ie: Scale the model up.