I've always favoured 25mm tubed scopes to 30mm.
My perception is clearer sight picture from 25mm than 30mm tubes, this includes high end models like Luep's etc too. I don't know why this is or if it's just me, but 30mm always appears more noisy (in the clarity) but I will be sticking with 25mm until a side-by-side comparison with the same spec in 30mm actually proves to have an advantage.
I have never required the additional adjustment which can be achieved by the 30mm tubed models, quite why you would want to move the picture even further from centre, I don't know.
I also agree that the new Mamba is clearer than the equivalent Viper model
MTC, take note, please offer more models in 25mm