Having owned an R5 and R6 (in addition to many other Icom products), as well as the Uniden 125AT, in this similar bracket the 125 wins hands-down for a number of reasons.
Don't get me wrong, the R6 is a great radio (albeit with one major flaw for me), but from an operational standpoint, you had better be willing to live / use it every single day to master the complex operational structure. I did - but a few months later - good luck remembering it all.
Memory management and superior alpha-tagging over the R6 is just one feature. Not having to buy custom software, and a custom programming cable are another. With the 125 you get the software free, and the cable is just a standard usb cable. If you lose it, just get another from practically anywhere around the house. And there is no question that the display on the 125 is drastically easier to read since it is about the size of the R20 physically.
Neither radio is a dog in the performance department. However, if you plug the audio cable from the R6 into say a typical mobile stereo input, you'll immediately hear the power-saver ticking away. That forces you to disable that feature. It is not known if Icom will ever fix it. The earlier R5 did not have this problem. The R6 also uses a mono jack, forcing nearly every modern user to have a huge adapter on the end of it for stereo phones. The 125 comes out of the box set up for stereo - although thankfully there is NO desense-prone FM broadcast reception.
The 125 allows for free firmware updates, and the latest improves upon an already good product. Try upgrading the firmware for your R6.

Or for that matter, finding online support from the vendor directly in the forums. You get that right here with Uniden.