These two are different in many ways, but at the end of the day, most of what you can do with one can also be done with the other just as well. Try to go to a camera and handle both, see if one feels more comfortable to hold; that can make a bigger impact in the long run than most other factors.
If you have some types of lenses in mind that you'll want to use, sooner or later, make sure that such lens is available for the camera, with an optical quality you find good enough and a price affordable.
Read up on equivalence to make better comparisons between the two, considering their sensors are of different formats/sizes.
And I'm sure this goes without saying, but don't buy a camera before you read the full review — every word of it, every sample photo, every comparison. I like the full reviews on this site, and I also like the work Gordon Laing does on
Camera Labs.