I've got both. Honestly I prefer ST Pro. I've only owned it a couple of months so it still has the "new" pin aura. I'll have to see how I feel in a couple of months.
I really like the speed and flow of the game. The speed is so intense. Combine that with the light show and it's really incredible.
In my case, the previous owner put some fantastic mods on the ST that really improve the game in my opinion. I have the Aurich (spelling might be off here) translite and speaker panel art. But what really makes it pop is the Pinball Refinery LED backpanel and speaker kit. The lights are tied to the modes and it's simply amazing. Combine that with the shaker motor and the whole experience is on another level. I love it!