Fry's >>>>>>>> Microcenter in terms of everything geek.
Microcenter >> Fry's in terms of computer related items.
Darned concise start, but I'd go a few steps further in the differences, such as: (And this is based on my admittedly limited experience with Fry's.....I've shopped the 2 Fry's in ATL vs. 2 MC's in ATL, 1 MC in VA, 2 MC's in MD, 1 MC in NJ and 1 MC in Boston.)
Microcenter >>>>>>>>>>>>>>>>>Fry's for customer service, ease of returns, not trying to sell previously used product as new, friendliness of the staff, lack of obnoxiously fanboy-ish salespersons who diss on you if you choose a brand that's not their favorite (listened to a pair of Fry's sales boys berating a customer for wanting to buy an Intel setup vs. an AMD setup), among other areas.
And I'd make the difference between MC and Fry's larger on computer related items......Fry's has a horrible selection of fans, watercooling items (MC carries more of the all-in-one WC'ing setups than Fry's and also has everything you need to set up a pieced together WC'ing setup---something Fry's doesn't even offer), fewer motherboards (not all MC's stocked motherboards are on the floor--you have to ask for the very expensive boards), and power supplies.....heck, maybe even video cards.
Fry's comes off as what Best Buy wanted to be but never understood how to accomplish it. Microcenter comes off as a retail Newegg, at least back when Newegg was just computer/geek items.
The absolute best computer/computer junk shopping experiences have been in Microcenter, no comparison. And, at least in my eyes, Fry's lost a lot of its attraction when they quit with the good mb/cpu combo specials they used to sell years ago.....