Pete
I think you need to clearly define what this new machine will be used for. To be honest, if your main market is residential, a D/F, Challenger, Tex etc would be too heavy and cumbersome to be used on many jobs. And carrying upstairs is a right pain.
Some people find it difficult to use an OP machine, and others can't get on with a rotary, so make sure you're comfortable with your selection.
For myself, I use my Low Moisture heated pad system primarily for commercial and as a problem solver for residential. I rarely combine HWE and padding. As Mike says, the pad doesn't feel very warm but this is because it is designed to not hold heat very well, so the heat passes through to the carpet, which then cools pretty quickly afterwards too. If you used a cotton pad, it should feel warmer for longer.
Safe and happy cleaning

Ken