Depends on the platform.
When I'm on iOS I use RadarScope. I run it most of the time on my iMac too. I have a paid data feed from Allisonhouse.
Sometimes if I'm on a desktop (and I have Parallels on my Macs) I run GRLevel2 Analyst, also with the Allisonhouse feed.
They have slightly different needs for me. If I'm just checking the radar a lot and panning/zooming all around while multitasking, I love the ease-of-use of RadarScope. If I am sitting in front of my iMac in "storm mode" fully dedicated to weather watching, I'll open-up Gr2 and work with that. My only hangups with Gr2 is that it does take a little more work/clicking and I can only pin one location + home, whereas on Radarscope I have multiple locations saved all over the country that I can jump to in a pinch.
FWIW Radarscope does not look great on my Samsung Tablet (Android), so it's rarely used.