First, why did I switch? I had a lease on a CLA and after the first year, I had put more than 24,000 miles on a 15K lease. I needed to get out. Also, my CLA was a FWD without bi-xenon/LED, so I wanted to upgrade. My intention was to get a 2015 CLA, but I was at a MB dealer that had an Edition 1 GLA and it had everything I wanted and looked great, so I talked to my dealer (which is 1/4 mile from my condo) and they found one for me.
Now to the comparison. They're very comparable. I think the ride is more comfortable on the GLA, but the CLA gets much better gas mileage. So far I'm getting 5 MPG less on the GLA than I did on the CLA. Seems to handle just as well. Now, they are vastly different cars, FWD vs. AWD, 17" vs. 19" wheels, no bi-xenon/LED on the CLA so comparing them is tough.
Bottom line, I liked the CLA, but I like the GLA even better.