I'm a little biased, but it's AdvancedHMI. The reasons I prefer it:
- I can make it do anything a PC can possibly do
- No runtime fees or tag based licenses
- Free development environment
- Runs on standard windows hardware, so if the hardware fails, a simple laptop will get you through until hardware is replaced
- Runs on low cost hardware (15" panel mount touch screen with Win7 is about $1300)
- Since it is based on .NET, the support community is probably an order of magnitude greater than the most popular dedicated HMI software